Two-flats

[_Shorty]

I had been waiting until I can get certain testing done before I posted anything about my Winchester 52D benchrest gun, but at least a couple people have asked for some info on it in one of the tuner threads, so I figure it wouldn't hurt to at least post some up-front info before I get around to posting all my findings. I haven't even finished all the testing I want to do, but I guess I can just add more info down the line anyway. Here's the gun in question, sitting on my PQP one-piece joystick rest:

(Click any image for a larger version, if there is one.)


It's a Winchester 52D action originally made in 1964. I still have the original barrel here, which had been set back and rechambered at some point, but it obviously is not what's on the gun now. What's on there now starts at pretty much the same diameter as the action and then tapers down to 1" at 4" ahead of the action. From there it is a 1" straight barrel. Hmm, well, sort of...



Looks a bit weird, eh? Here's the muzzle end.



At the 4" mark it drafts down to 0.643" with an equal amount taken off both the top and bottom of the barrel. This continues until it drafts back up to a 1" cylinder again for the remainder of its length. You can see here how it is flat on the top and bottom for its entire length between those points.



I have a Sightron SIII 10-50x60 mm scope on it with fine crosshairs and a 1/8-MOA dot, which has 1/8-MOA clicks. It is in a benchrest stock with a 3" wide fore-end, of a manufacturer that's unknown to me, but may be an old McMillan model.





It was pillar-bedded by whoever originally put it in this stock. Unfortunately, though I know who the previous two owners were, none of us knows who did the work on the gun.



Whoever did it seemed to do a pretty nice job, anyway. The underside looks nicely done, too.



Here's a shot of the barrelled action.



I don't know if the person that did the work of mating it to the stock also did the rest of the gunsmithing on it, but whoever worked on the factory trigger did a nice job, as well.



So, I'm sure pretty much everyone looking at this will be thinking something along the lines of "Well, what's the deal with that barrel, anyway?!" The answer is pretty simple, really.



That darn Sightron was so big it wouldn't clear the barrel, so I had to mill off some of it to clear the bell end of the scope.

Alright, alright! No, that's not actually the answer. Hehe. But whenever anyone asks me about it that answer tends to get at least a chuckle, and/or a strange look. So, the reason I popped into that tuner thread with a picture of it was because the design of the barrel is actually related to tuners and/or barrel tuning. Some of you may have run across Varmint Al's website in the past. Here's a link to one of the pages that actually has to do with tuners where about halfway down he mentions this barrel design. He used some "finite element analysis" software at work, when he was still working, to simulate a rifle and through some trial and error came up with this design. I'll share a few of his pics, but if you want to read even more you can go to the second link on his site that I just mentioned.





And the profile in the middle section.



And now to the meat of the matter. I'll share this graph and then talk a bit about it.



So, what you're looking at there is the elevation on target that the barrel is aiming at versus time. And at the 0-second mark is the start of ignition. As the primer goes off, and powder starts to burn, and the bullet starts going down the barrel, all those things start affecting the spot on target where the barrel is aimed. The graph is comparing two barrels. One, a typical reverse-taper contour barrel that was popular for a little while in benchrest circles down in the USA. And the other, the theoretical two-flats design that he was working on. Al said to me that he never actually had one of these barrels built, and to his knowledge nobody else had tried one, either. He was pretty surprised and excited when I sent him some pictures of it installed on the gun after I got it back from the gunsmith.

 

[_Shorty]

Anyway, back to the graph. So the lines correspond to each of the two barrels, but also what is going on with one example shot that ends up having a muzzle velocity of 1035 fps, and a second shot that has a MV of 1075 fps. And there are two vertical dotted lines on the graph, one red, one blue, that correspond to where in time the two example shots will ultimately leave the muzzle. Going back to the aiming-point lines, the light/dark green lines being for the reverse-taper barrel, and the red/blue lines being for the two-flats barrel. You can see that both barrels having rising and falling aiming points on the target depending on where you look, time-wise, before the bullets exit the muzzle at each of the vertical dotted lines. You'll need some understanding of what tuners can do for you, and what positive compensation is with regard to that, in order to appreciate what's going on there. What's important to note is in both cases the barrel is in the middle of an upswing when both shots exit. The 1075 fps shot leaves earlier, and is therefore aimed slightly lower than the 1035 fps when it leaves at a later point in time.

If you examine the green lines you can see that the reverse-taper barrel is actually moving too fast to properly compensate for the differences in muzzle velocity of the two shots. It is swinging upwards, but at a rate that is too fast, and the result is the 1035 fps shot will hit the target someting like 0.13" too high compared to where the 1075 fps shot will hit. This isn't disastrous, because a tuner in the right weight range will slow the barrel movement down, and if you get it right then you will slow it down just enough so that the upswing rate will make both shots in the same spot. Now, if you look at the red/blue lines for the two-flats barrel you'll see that the untuned difference in elevation for the two shots is much less than that for the untuned reverse-taper barrel. Here, we only see about 0.03" of difference in elevation between the two shots. Both shots are exiting during an upswing, just as they were for the reverse-taper barrel, but the rate of upswing is closer to the ideal for a 50-yard target than the reverse-taper barrel's rate of upswing. And you could also bring it closer to the optimal upswing rate with a properly chosen tuner to match its characteristics. Horizontally it is still nearly as stiff as a 1" cylinder, and only more flexible vertically.

So why would you want to choose one over the other? Or would you even want to choose one over the other? Well, take a look at the green lines again. And keep in mind that a tuner will slow down what the barrel is doing. This does two things with regard to that line. It slows down what's happening, essentially stretching that line out to the right side of that graph, and it also lowers the magnitude of what's happening due to the added mass, essentially squishing the line in the up and down direction closer towards zero. If you look just to the left of the vertical red/blue muzzle exit dotted lines you will see that the muzzle changed directions quite recently. You desperately want to avoid having any shots exit the muzzle while the barrel is swinging downwards. An upswinging barrel reduces vertical at the target. A downswinging barrel increases vertical at the target. So in the case of the green traces we see there, if you go a little too heavy with your selected tuner mass you're going to move that downswing over to the right and possibly push it into the muzzle exit range. The downswing there is relatively small, but you want to avoid it altogether. If you add too much tuner mass then you'll move that downswing over between the dotted exit lines and introduce more vertical into your results on target, which is what you're trying to avoid in the first place. You *might* be able to keep adding more mass and get past that downswing and into the previous upswing, but as I say, adding more and more mass also reduces the amplitude of those up/down swings, so you might also make it even harder to tune. That's if you could even get past that downswing portion. You may or may not be able to do that.

Yeah, I'm rambling on and on, but it is a pretty deep topic, tuners and tuning. And the point of Varmint Al's two-flats design is to attempt to make it easier to tune in the first place by bulding in some desirable characteristics right from the get-go. If the barrel itself is already fairly close to tuned with nothing on it then you shouldn't have to do as much to make it behave even better. One of the reasons for the two flats being milled into it is to actually make it easier for the barrel to swing in the up and down direction for a longer period of time. If you compare the red/blue traces to the green traces you can see how it seems to be in an upswing for a much longer period of time than the reverse-taper barrel, both before and after the muzzle exit times. And if you look just to the left of the red dotted line you can see how it is a lot flatter not too far to the left of that line. What this indicates is it will likely be possible to find a very nice tune with very little tuner mass. I've played with a few.



There are over 50 there, and that's not all of them. Hahaha.

What I learned immediately was that my Harrell tuner was way, way too heavy. And I figured that out by using two different speeds of Eley. The velocities that Eley lists on their boxes are not what you're necessarily going to get with your barrel, but in my experience you will see a similar difference between two different listed speeds even if it isn't close to their listed value. If you pick two lots that have average speeds listed that are 20 fps apart you're likely going to also see a difference of fairly close to 20 fps in your barrel, even if your barrel is faster or slower than their test barrels that give them their average velocities. So if you select the fastest and slowest lots available to you to do this kind of testing it can really save you a ton of time. Shooting a practice BR50 target (which is like the ARA target) gives me a 25-shot group with a calculated offset from the aiming point. Doing this with two different speeds/lots should give me a different offset for each, since they will have different average velocities. Comparing my results with no tuner to that with the Harrell installed showed me nothing but bad news on target, and had an unhelpful elevation offset. It wasn't doing anything helpful, and so I had to figure out a way to either lighten the Harrell by a whole bunch, or find another way to attempt to determine how much weight I needed.

 

[_Shorty]

Enter my 3D printer.

I printed a big unthreaded nut that would be a tight slip fit on my muzzle. And proceeded to shoot groups/targets while slowly adding more and more weight via automotive stick-on wheel weights, which gave me 7-gram intervals to test with. I found more than one area of interest to revisit. I also printed small clamps similar to the Harrell clamp, and made them with smaller and larger outer diameters. And also with threaded sections to add washers. I printed 1-gram washers and started testing with those, too. This also yielded some potential happy zones to check into further. So far I seem to have found at least two regions that show the most promise with this barrel. One being somewhere in the 13-15 gram region, likely very near to 14 grams, and another out around 100 grams, possibly in the region of 102-106 grams. Up until now, most of my testing had been with a lot of Eley Team that I had managed to score tons of 2250/2500 scores in practice, and even a 2350, as well as some 2200+ scores in matches, including a 2300 that would've been 2350 if I had slightly less zero offset. Doh! Hehe. I recently received a case of Eley Tenex after testing five different lots of the stuff. The majority of the case is the remaining stock that my supplier had of the lot that shot best for me, and I then asked to fill the rest up with one of the lots that shot almost as good but also had a fairly different listed velocity. So, I am now waiting to get out to the range to conduct further tests now that I have some ammo that should be better than the Eley Team that I had pretty good results with already. Unfortunately for me, I am now at the mercy of the club having to make substantial changes to the range in order to make the CFO happy. So, I twiddle my thumbs until they can get that work done and we can start shooting at the 50-yard line again. For the moment, all we have available to shoot is the 100-yard line, but that does me no good with a rilfe that's shot in competition at 50 yards and is actually engineered to work best at 50 yards. Yes, its very design means it introduces more vertical at 100 precisely because it tries to reduce vertical at 50 yards as much as possible. That is what barrel tuning gets you, the best results at one distance, at the cost of worse results at other distances. You can only get rid of as much vertical as possible at one distance. That's just how it works.

I've also drawn up a copy of the Harrell and printed some with varying total masses. I've done a lot of playing with PRx tubes. (Google Purdy Prescription to find some info about that on RFC and elsewhere.) I've figured out whether the PRx tubes are actually doing anything, and what they're actually good for. They are actually helpful, but I don't believe they help in the way that Purdy thinks they do. In my opinion, they're a helpful addition to weight tuning, not a replacement for it. And so I've printed up a bunch of those in different configurations, some with threaded ODs to play with washer weights. So far, I've shot my best targets with a fixed tuner that weighs just over 14 grams and utilizes a 5th-harmonic PRx tube. I have also been playing with something around 100 grams lately, but as of yet haven't had the same amount of shooting with that range of mass. With the ~14-gram example so far I have shot many targets over 2200, including this best so far target of 2300 in one of the BR50 matches that would've been a 2350 with slightly less zero offset that I mentioned earlier.



And here's some stats for that combined into one 25-shot group.

So hopefully I can get out to the range soon and start playing with the Eley Tenex. I'm kind of thinking I may need to play around with the ~14-gram tuner again, since I had pretty good luck with it and the lot of Eley Team that I had. With so many scores over 2200 with that it wouldn't make sense not to try it out again with the Tenex. I had been playing around with some Lapua Center-X when I found there might also be something to look at around the 100-gram mark, but while I will give that another look with the Eley, I'm kind of thinking it might be better with the lighter one. I'll see once I can get out there again.

So why might you not want a barrel like this? Well, like I say, it is inherently designed to only shoot best at 50 yards. It might shoot acceptably at other distances, but being tweaked to reduce vertical at 50 yards means it'll always show its best at that distance, and will introduce vertical at other distances. It may or may not be enough to worry about, but for me it is only a 50-yard competition gun anyway, and that was the only reason I even bothered to try it. I must say I'm not yet convinced that the barrel is actually a good one. And I am not referring to the design, but rather, just talking about whether or not the people that made it can make a competition-worthy bore in the first place. I had a heck of a time trying to convince anyone to even make it for me. Eventually I ended up having it made by some people that I didn't even know made barrels, and I'm not even sure how much they themselves are involved in the making of their barrels. For all I know it is just an off the shelf blank that they turned and milled. I don't know if they were the ones that drilled it, rifled it, and did all the other bore prep work or not. I know what I was told, but I don't know if what I was told was actually what happened. I would've loved to have had it made by a well-known barrel maker with a proven competition track record, but none of them would bite. So I may or may not have a good shooting barrel worthy of benchrest competition. I have seen many scores over 2200, and small number over 2300, so maybe it isn't actually half bad after all. I'm going to wait until I get a bunch of that Tenex down it before I make up my mind on that one, though. In the end, I could throw the original barrel back on there. It shot pretty well with it, too. And I have a heavy barrel that I think was pulled off of a 52C that I haven't tried yet. For now, I'll play with this one some more, as soon as I can actually get out on the range again. I'll likely post updates in this thread as anything that warrants it comes up. Feel free to ask any questions.

 

[grauhanen]

Thanks for sharing information about the two flats barrel, Shorty. I thought it looked somewhat familiar but didn't remember it was like the one in Varmint Al's web page. I wonder why similar barrels aren't seen more often.

In recent years some shooters have been using Harrell tuners that have been slimmed, wasp-like, to about half their original weight. They report good results with them. Of course, as readers may know, the standard barrel dimensions with unreduced Harrell-type tuners still dominate the RFBR scene south of the border.

 

[45CAT]

At one time that barrel shape was put on “running boar “ rifles. Can’t remember whether it was on an Annie or Feinweinbach ( spelling ?). I think IBI calls it their “Olympic” ( spelling again, it’s gonna be a bad day ) style

 

[Mystic Precision]

Shorty, very cool info. There has been some really good insight on tuners and barrel tuning lately (over the last few years) as it applies to LR shooting. Giving a modern explanation to science tested over 100yrs back.

In brief, the 'taming' of the barrel swing can be very 'positive' (sorry, couldn't help myself) for LR shooting as well.

If you look at the barrel swing graph, the benefits of reducing vertical at 50yds ALSO keeps the bullets in a tighter vertical pattern further away. Depending on the max distances desired, you may or may not INCREASE the vertical a bit at short range to get the 'cone' to be tight all the way down range. If you want to get a tight downrange cone, start your tuning at 100yds.. then finalise at 200yds.

Ideally, the ammo is made to tighter standards so the variations between rds approaches zero making this barrel tuning so much easier, but with rimfire, that is not going to be the case. Here, control of the barrel position relative to variations in ammo exit is the key.

The more the ammo varies... the more positive compensation is helpful.

Ever try putting weights ON the flats?

Jerry

 

[_Shorty]

Thanks for sharing information about the two flats barrel, Shorty. I thought it looked somewhat familiar but didn't remember it was like the one in Varmint Al's web page. I wonder why similar barrels aren't seen more often.

In recent years some shooters have been using Harrell tuners that have been slimmed, wasp-like, to about half their original weight. They report good results with them. Of course, as readers may know, the standard barrel dimensions with unreduced Harrell-type tuners still dominate the RFBR scene south of the border.

Surely, K.I.S.S. applies, not to mention cost. While the idea seems to accomplish what it sets out to accomplish, it is obviously more complicated than a typical barrel, and the extra work meant it was somewhere in the neighbourhood of 2-3x as much as a typical barrel. So when people are capable of wringing great results out of more typical barrels it can be harder to justify spending 2-3x the money if you're only going to achieve similar results anyway. Guys down in the States have put up a lot of incredible scores with straight contour barrels, and I'm sure they'll continue to do so. If it ain't broke...

This barrel involves a lot more work than the typical barrel installation job. With a simple, typcial rebarrel job you take a blank, probably contoured already, and thread it, crown it, chamber it, and fit it. Job done. With this barrel it gets more complicated. And ideally, the barrel maker would be involved early on. This is one area where I am a little suspect about my barrel. If it was cut-rifled, as was claimed, then some of my worry goes away. If it were actually button-rifled then I have concerns about the bore dimensions with no easy way to confirm or deny that they are what they should be. Getting this kind of barrel done right involves quite a few steps. Obviously the flats need to be timed so they're actually on the top and bottom, and not at some random angle. So the blank needs to be fitted to the action in order to determine where to cut the flats. Even in the case of a cut-rilfed barrel, ideally you would do this and then do the final bore lapping. I doubt this was done in my case, though it may have been. This is to ensure that if the bore does happen to change shape after cutting the flats that it can be trued back up during lapping. A button-rifled bore is likely to be a little messed up after having flats cut in it like that, but a cut-rifled bore probably shouldn't change much, if at all. It might change slightly, but whether it did or not, doing the final lapping afterwards will stop that from mattering anyway. Then it can be chambered, crowned, and installed, finally. Quite a bit of extra work compared to a regular rebarrel job, and you'll see that in the bill. I believe it ended up being over $1,350 from them, and they even screwed up on the chamber depth I specified to use with my reamer. Luckily for me they went too shallow, and I took it to another gunsmith to have it cut again, slightly deeper to the dimension I wanted. When the other gunsmith got it he wasn't happy with how they fit it, either. He ended up shaving a few thousandths off the breech face so the bolt would actually close nicely. He actually mentioned this to me before he did that portion of the job, and I got to check it out before and after, and I was kind of pissed at yet another mistake from the first place. Oh well. He fixed it up anyway. That work should've been unnecessary, and pushed my end up over $1,600 now. Though that shouldn't count, as it was correcting mistakes. Even so, as I say, the original price is way more than the typcial barrel would cost. I would still love to get the likes of Shilen or Benchmark, or any of the other well thought of barrel makers to make one of these to compare it to, but I couldn't talk any of them into it. Shilen was the closest to agreeing, but lost interest after finding out it would ultimately be shipped to Canada. They didn't want to bother after that, even if the importing and exporting stuff was left to a third party and they didn't have to deal with any of it. Which was a shame.

 

[_Shorty]

At one time that barrel shape was put on “running boar “ rifles. Can’t remember whether it was on an Annie or Feinweinbach ( spelling ?). I think IBI calls it their “Olympic” ( spelling again, it’s gonna be a bad day ) style

I wouldn't be surprised to learn that barrels with flats milled into them have existed before. But in this case, and for this purpose to be met, it requires using carefully calculated dimensions in order for it to behave in the desired manner. It requires a certain overall length, a certain thickness for the flats, a certain contour before the flats, and a certain contour after the flats in order for it to provide the desired amount of movement and rate of movement with which to produce the desired results at 50 yards. Anything other than that is going to behave in a different fashion. While some random barrel with some random flats might exhibit some different behaviour from a barrel without them, the chances of it exhibiting all the traits that this one does is pretty slim. All the dimensions involved with this barrel play a part in dictating how it behaves during firing, what it does, and how much it does it, and how quickly it does it, and any of the dimensions being different will change that behaviour quite a bit. And it doesn't take much to drastically change how a barrel behaves. One day I set up and began shooting and the thing was not cooperating at all, and at first I was pretty confused. I was using one of the tuners I had already had pretty good results with, and checked the settings to make sure I hadn't inadvertently moved something, and everything was fine. Then, right after double-checking the tuner, I spotted the problem. One of the things I regularly do to help make sure everything is repeatable is ensure that the gun is level. (This was before I received my one-piece rest, which has its own level built into it.) I have a little circular bubble level that I would place on the barrel flat to help make sure I've got my front rest set up so the gun is level left to right. And apparently I had forgotten to remove it from the barrel that morning. It only weighs 31.1 grains. And it simply sitting on the barrel like that not only moved my point of aim by a rather surprising amount, it was shooting quite a bit worse than usual, too. So, at least in my head, a barrel that has drastically different dimensions than this one isn't very likely to exhibit the same behaviour if mine could go haywire with just 31.1 grains of plastic and liquid resting on top of it. Varmint Al said it took quite a bit of playing with all the various dimensions in his simulation software before he got to the final design with the behaviour he was after. And from what I've seen on paper with all the testing that I've done with it in the real world, I don't doubt that changing any of the dimensions by any large amount would drastically influence the results. Or changing any of the dimensions by even by small amounts.

Funny that you say IBI has something similar. They were among the manufacturers I asked and were uninterested in the job. If they did something similar at one point they don't seem interested anymore, and I don't see anything listed in their current list of available contours that is anything other than what's typically available from anyone. Although, I think perhaps you're just misremembering with the running boar rifles. I have seen pictures of some running boar rifles that simply had a contour that got larger at the muzzle end, while were still just typical barrels in all other ways. No flats milled into them. Still round from one end to the other. They just had a larger muzzle end, which I imagine is simply an attempt to slow down the muzzle movement in much the same way as a tuner does. I imagine that would indeed slow the movement down, though I have no idea how much tuning they may have done in those designs. My barrel doesn't actually get larger at the muzzle like those did, though. After the initial contour at the action end it is 1" straight the rest of the way, ignoring the milled flats.

 

[_Shorty]

Shorty, very cool info. There has been some really good insight on tuners and barrel tuning lately (over the last few years) as it applies to LR shooting. Giving a modern explanation to science tested over 100yrs back.

In brief, the 'taming' of the barrel swing can be very 'positive' (sorry, couldn't help myself) for LR shooting as well.

If you look at the barrel swing graph, the benefits of reducing vertical at 50yds ALSO keeps the bullets in a tighter vertical pattern further away. Depending on the max distances desired, you may or may not INCREASE the vertical a bit at short range to get the 'cone' to be tight all the way down range. If you want to get a tight downrange cone, start your tuning at 100yds.. then finalise at 200yds.

Ideally, the ammo is made to tighter standards so the variations between rds approaches zero making this barrel tuning so much easier, but with rimfire, that is not going to be the case. Here, control of the barrel position relative to variations in ammo exit is the key.

The more the ammo varies... the more positive compensation is helpful.

Ever try putting weights ON the flats?

Jerry

I'll start with the last question first. Or rather, read my reply to 45CAT, specifically the part about forgetting to remove a 31.1-grain bubble level sitting on it. Hehe.

As for vertical at other distances, let's again return to the example in the graph. It used shots at 1035 fps and 1075 fps, so let's calculate the induced vertical at distances other than the tuned distance. (I figured out how to get more than one decimal place with the JBM calculator now. Yay! Hehe.) Some crazy guys shoot 22 LR out to 500 yards, so why not see what happens when you tune at 25 yards, 50, 100, 150, 200, 250, 300, 400, and 500? That'll give a few half/double examples to look at, too. Units are inches.

You may notice a couple of patterns there. When you're talking about distances between you and the tuned distance the induced vertical grows until you reach the halfway point and begins getting smaller again past that, until it ultimately reaches zero at the tuned distance. And beyond the tuned distance the error just continues growing and growing the further you go. If you will be shooting multiple distances you could choose a compromise with an acceptable amount of induced vertical, and just live with it. But if you're only going to be shooting at one distance you are obviously better off to actually tune at that distance. This is why I don't understand it when I see F-Class shooters that will shoot at 1000 yards in competition working up loads at 100 yards or 600 yards or any other distance besides 1000 yards. You can accept a compromise, but if you want the best results you can possibly get you have to tune at the distance you'll be shooting. This would mean multiple loads if you're shooting at 1000 yards, 600 yards, etc. One load and tune for each distance. Unfortunately, barrel life isn't infinite. You might only be able to afford to work up one load and get as many competitions out of that as possible. Otherwise you're going through barrels even quicker. But if you had the money and didn't mind spending it, you'd want a load for each distance, as well as a tune to go with it. $$$

edit: Added a line on the last chart here for the average induced vertical values when tuning at each distance. This lets you see that in this particular case the best compromise would be to tune at 300 yards, as this would give the smallest average for induced vertical at all distances.

 

[grauhanen]

At one time that barrel shape was put on “running boar “ rifles. Can’t remember whether it was on an Annie or Feinweinbach ( spelling ?). I think IBI calls it their “Olympic” ( spelling again, it’s gonna be a bad day ) style

Running boar rifles don't have barrels that have "two flats" -- that is, a "flat" top and "flat" bottom (as opposed to round).

These rifles have round barrels that often have a removable barrel weight at the muzzle. Below is an image of Walther Running Boar (sometimes called Running Target) models. Anschutz Running Boar models look similar.





The barrel shown by Shorty has "two flats" which end about four inches before the muzzle, which may give an appearance of having an "extra" large muzzle area. It is in fact no larger than the original 1" diameter of the barrel prior to being flattened by having material removed.

The IBI barrel referred to may be one of those shown below, perhaps the second from the bottom. It is profiled to have a "bulge" in the muzzle area. These barrels are round.

 

[Mystic Precision]

Shorty, as someone that competes out to 400yds with rimfires and has tested LR in both centerfire (way out there), the useage of velocity spreads as an indicator of downrange vertical/grouping is greatly flawed... small ES/SD doesn't not mean super tight LR groups. In fact, you can have a range of good and bad systems with nearly identical ES and SD numbers. Pretty sure, you had an example of this in a spreadsheet and targets.

My testing of a number of rimfires to 500+yds has demonstrated that getting good 100yds grouping... confirming at 200yds, will typically lead to excellent downrange results that can be much tighter vs the predicted ES/SD suggest.

Now there are other variables on why a system might fail beyond 200yds but monitoring velocity variations is not going to predict much of anything.

And of course, that can vary from rifle to rifle... ammo type to ammo type.... thus, any metric (ES/SD in this case) that is not 100% reliable in what it is telling me, isn't worth my time to monitor.

Jerry

PS.. as a competitive F class shooter, competing with the same load from 300yds to 1000yds, tuning for this is no problem. A typical top level f class rifle will shoot in the 2's and 3's, and maintain that level of consistency at all distances. Obviously, this is not BR competitive but as I said earlier, there are compromises where you adjust your tune a little 'worst' at shortedr range, to maintain that tight cone of accuracy all the way downrange. And I most certainly don't recommend load tuning at 100yds... 250 to 300yds are nice if you have the facilities. I have also done final tweak at 1000yds.. but by this point, gains are very small (or maybe more in the mind of the shooter)

 

[_Shorty]

But this disconnection between MV and POI isn't happening for no reason, nor some unknowable reason, nor magic. It is directly related to barrel vibrations. The way the barrel is vibrating is changing the launch angle, and thus the POI. Let me ask you this:

If you shot a 1000-yard target and your group size out there happened to be 1 MOA, what would the group size be at 250 yards, 500 yards, and 750 yards for those same shots? Say you had four electronic targets set up so that the bullets all went through each of them and you could actually get group sizes at the four distances at the same time. One target at 250, one at 500, one at 750, and one at 1000, and a single shot went through them all in one go. Do you think that 1 MOA group at 1000 also be 1 MOA at 250 yards, and 500 yards, and 750 yards?

 

[grauhanen]

Shorty, as someone that competes out to 400yds with rimfires and has tested LR in both centerfire (way out there), the useage of velocity spreads as an indicator of downrange vertical/grouping is greatly flawed... small ES/SD doesn't not mean super tight LR groups. In fact, you can have a range of good and bad systems with nearly identical ES and SD numbers. Pretty sure, you had an example of this in a spreadsheet and targets.

My testing of a number of rimfires to 500+yds has demonstrated that getting good 100yds grouping... confirming at 200yds, will typically lead to excellent downrange results that can be much tighter vs the predicted ES/SD suggest.

Now there are other variables on why a system might fail beyond 200yds but monitoring velocity variations is not going to predict much of anything.

Once beyond 50 yards it becomes increasingly difficult to accurately predict .22LR trajectory. At 100 yards it's not simply twice the group size achieved at 50. Excluding the influence or wind or air movement between shooter and target, there is the obvious reason that flight time to 100 is more than double what it is to half the distance and gravity will exert its inexorable effect on all falling objects. As a result, muzzle velocity variation will play a role that's unavoidable.

What is important to remember, however, is that all predictions generated by ballistics calculators are themselves based on trajectories achieved with .22LR bullets that are perfect in terms of symmetry and center of gravity. (This is the only way ballistics calculators can function.)

The problem is that, unlike jacketed centerfire bullets, soft lead projectiles such as .22LR bullets (airgun pellets, too) are very difficult to manufacture with close to perfect centers of gravity. Some lots of .22LR match ammo will be better or worse than others, some bullets within a lot will be better or worse than others.

With center of gravity imperfections that vary, the bullets don't have trajectories that are consistently predictable. It leads to at least two things. One s that ballistics calculator predictions don't hold. The other is that group sizes can vary unpredictably, regardless of what MV predictions say they ought to be.

It's worth noting here that it's not simply bullet center of gravity imperfections that contribute to unpredictable group size. There's something else at play. The .22LR bullet obturates according to each barrel's unique chamber/leade/bore. That obturation itself plays a role in establishing the bullet's center of gravity when it leaves the muzzle. Some rifles will affect the bullet ultimate center of gravity for better or worse. The result is that some rifles that shoot well at 50, don't do as well at 100. Similarly some rifles don't shoot the same lots of ammo at 100 as well as another rifle. In other words, an ammo that shoots well at 100 in one rifle may not do well in another.

To summarize, MV and ES plays non-exclusive role in determining results at 50, at 100 and beyond. It is only part of the explanation because bullet trajectory unpredictability increases with distance. At 10 yards, virtually all .22LR match bullets will go into the same hole without regard for center of gravity imperfection; at 25 yards virtually all very nearly go into the same hole, which grows a bit; at 50 yards gravity plays a more visible role as does center of gravity issues; at 100 and further both, especially center of gravity imperfection is obvious and undeniable.

Ballistic calculators (MV predictions) require perfect bullets to make sense. When .22LR bullets aren't perfect -- and they often aren't -- they don't have POIs that make sense.

 

[_Shorty]

Not just imperfections in CoG, but also simply in surface shape. Drag will vary somewhat due to dings and dents and other physical imperfections. There are all kinds of variables at play here. Even the wind on calm days varies enough from shot to shot to not be able to ignore its influence on POI. Lots of things that add up to some amount of random dispersion, to be sure. And one of the biggest influences is obviously where the tube is aimed at. Since that is one that we can exert some control over, it makes sense to put some focus on it. And, at least for 50-yard benchrest shooting, since groups from a well tuned rifle are fairly small and round it is likely safe to assume that where you've got the tube aimed is the most important factor to worry about. Since it is the one we have the most control over, that only makes sense anyway. All the other variables are still present in the case of a well-tuned rifle, yet you can make a nice round, ragged hole. Take it out of tune and the group gets uglier. I'd say that indicates we should focus the most on that aspect. Wind, bullet imperfections, etc., we have no control over. Wind is probably the next biggest worry, but at least we can try to read it and gauge when to fire and when not to.

 

[Mystic Precision]

But this disconnection between MV and POI isn't happening for no reason, nor some unknowable reason, nor magic. It is directly related to barrel vibrations. The way the barrel is vibrating is changing the launch angle, and thus the POI. Let me ask you this:

If you shot a 1000-yard target and your group size out there happened to be 1 MOA, what would the group size be at 250 yards, 500 yards, and 750 yards for those same shots? Say you had four electronic targets set up so that the bullets all went through each of them and you could actually get group sizes at the four distances at the same time. One target at 250, one at 500, one at 750, and one at 1000, and a single shot went through them all in one go. Do you think that 1 MOA group at 1000 also be 1 MOA at 250 yards, and 500 yards, and 750 yards?

Dialed in at 250/300yds, the competitive F class rifles will be in the 2's usually. By 1000yds, you are competitive while staying in the 3's (some will stay in the 2's)... this is no affect by winds. This is just the natural expansion of that cone.

so there is a change but much smaller then numbers would predict. The cone of accuracy for a competitive F class rifle is tight at all distances.

With properly set up rimfires, the cone of impacts at 300yds can be tighter then numbers would predict... somethings, much tighter.

What is the built in error of top tier chronographs like the labradar and magnetospeed? When the simple math of +/- is accounted for, the data just isn't as predictive as many would like.

Jerry

 

[_Shorty]

I don't know what you mean by in the 2s and 3s. Do you mean 0.2 to 0.3 MOA groups? Let's say for the sake of argument that you do have a rifle that'll shoot 0.3 MOA groups. "Expansion of that cone" seems to indicate that you think groups will stay pretty much the same size (MOA) at any distance, so if you are shooting 0.3 MOA at your test distance of 300 yards you will also see 0.3 MOA groups at anywhere you look from 100 yards to 1000 yards. So, you seem to be saying you'll see groups like this if you could look at all distances at the same time when you shot a 1000-yard 0.3MOA group:

Unfortunately, this goes directly against external ballistics. In order for shots to converge at some point they will have some elevation deviation at all other distances if they all have slightly different velocities. If you manage to shoot a 0.3 MOA group at 1000 yards and you could look at the group size of those same shots at every 100-yard increment it would likely look more like this:

That's assuming a 0.284 with MVs between 2840-2860 fps.

You seem to be stuck on whether or not shots hit according to where MV predicts they would. Again, barrel harmonics is a thing. Indications are you may not understand barrel harmonics well enough. As I just said, shots don't hit somewhere other than a MV prediction for no reason. They do so because the barrel was aiming them there. In the case of the rimfire 50-yard example, IIRC, we are talking about a difference of just slightly under 0.004" in muzzle displacement. You seem to have come to the conclusion that MV can't predict POI because MV predictions don't always match POI. And therefore, MV predictions do not work and should be ignored. Unfortunately, this is not the case. MV predictions do work. But you also need to know what the launch angle was. Your supposition that MV predictions do not work because they don't always match the POI only makes sense if you are assuming barrels are infinitely stiff and do not move at all. We both know that isn't the case. This is where you happen across a void of data. You can't know this launch angle information precisely enough because we are talking about requiring knowing extremely small amounts that vary somewhat every time. This is not the same as saying MV predictions do not work.

What it is actually telling you is that barrel movements are not easy to predict in relation to muzzle exit timing. But barrel movements can be controlled to a certain degree. That is, you can shrink the unpredictable window they move in somewhat, and improve your results on paper if you mange to do this well. They actually do move in a somewhat predictable fashion, but we are at war with timing exactly when the bullet exits the muzzle. With rimfire you're more restricted in what you can change. Barrel contours, barrel tuners, ammo brands/lines/lot numbers, basically. With centrefire you've got more control over more of the variables involved. You can then also throw in primers, powder, bullets, case prep, seating depth, etc.

In the case of this rimfire rifle, the design of the barrel is intended to try making that fight with bullet exit timing more easily managable than a typical barrel. I would say, though, that its cost likely outweighs its usefulness, considering you can get absolutely great results with a more typical barrel that costs much less. If you don't mind the cost, though, and can actually get someone to make one, it does seem to do what it is designed to do. I'm chomping at the bit while I wait for my club to get the range sorted out. I really want to get some of that Tenex through it. I do plan on redoing some of the tests I've already done with Eley Team in hopes of the Tenex behaving a bit more consistently, and hopefully showing even better results. I do plan on sharing some of those results whenever I can actually get out there. I think I should be able to show rather readily what it is doing and how the tuner helps it.

 

[grauhanen]

In the case of this rimfire rifle, the design of the barrel is intended to try making that fight with bullet exit timing more easily managable than a typical barrel. I would say, though, that its cost likely outweighs its usefulness, considering you can get absolutely great results with a more typical barrel that costs much less. If you don't mind the cost, though, and can actually get someone to make one, it does seem to do what it is designed to do. I'm chomping at the bit while I wait for my club to get the range sorted out. I really want to get some of that Tenex through it. I do plan on redoing some of the tests I've already done with Eley Team in hopes of the Tenex behaving a bit more consistently, and hopefully showing even better results. I do plan on sharing some of those results whenever I can actually get out there. I think I should be able to show rather readily what it is doing and how the tuner helps it.

Shorty, I don't know the answer to this question. If a "two flats" barrel made from a 1" blank is, say, .750" between flats, will it be less, equally, or more responsive to a tuner compared to a non-tapered round barrel that's .750" in diameter?

 

[_Shorty]

Shorty, I don't know the answer to this question. If a "two flats" barrel made from a 1" blank is, say, .750" between flats, will it be less, equally, or more responsive to a tuner compared to a non-tapered round barrel that's .750" in diameter?

I'm not sure how similar or dissimilar they might be. And I'm not really sure what you mean by less/more responsive. The trick to approaching an ideal amount of compensation is adding the right amount of mass to get its upswinging speed in the right ballpark. I think you should be able to do that with almost any barrel. It should be noted this is not the same as saying "Slap a Harrell on anything and it'll work." How much mass you add is very important, and that depends on the barrel's dimensions.

There will be a little more meat with the one that's been milled flat than the one that's round. I would imagine that will make it slightly stiffer than the round one. In my case, the difference between its flats and the diameter of a typical benchrest barrel these days (0.920" to 0.950" seems popular now) is obviously larger than when looking at 0.750" flat versus 0.750" round. So it probably makes sense that mine needs a different amount of mass compared to a typical barrel. But 0.750" flat and 0.750" round would probably be a lot closer in behaviour, with regard to vertical, perhaps with the flat one needing only a slightly different amount of added mass to achieve similar behaviour. I'm not even sure if it would need more or less added mass in that situation, but I think it would need slightly more since it should be slightly stiffer. One of the reasons for taking this two-flats route versus simply finding a diameter for a round barrel that works well is that you still have a much stiffer barrel horizontally with the two-flats route. We do want some movement vertically because that's how we compensate for differing MVs, but we also want as little horizontal movement as we can get. And that's what the two-flats design helps you reach.

I think one of the keys, no matter the design type, is you must start out with a barrel contour that moves too fast, because you can't do anything to speed up a barrel that's too slow. It might be safe to say that practically any barrel is already moving too fast, though, I think. It might take some weird doing to make a contour that's too slow. Anyway, then you need to determine how much mass to add to slow it down into the sweet spot. How much mass will vary depending on the barrel's characteristics. So far I've played around with four different barrels, two on this gun, and two different guns a friend owns that I helped tune. All four examples were different from each other in contour/design/length, and each needed quite different amounts of added mass before they seemed to be in the sweet spot. I think I mentioned this before, but using two different lot numbers of ammo that have fairly different listed muzzle velocities is a good shortcut to finding the right coarse region, after which you do your fine tuning with a single lot number. Shooting groups/targets with two different speeds should give you two different calculated average centres for POI. Changing the amount of added mass should move this average centre point up or down. Get them to converge and you're in the right ballpark. Then you can begin fine-tuning from there to get the best results with a single lot number. You can find the right ballpark without two lot numbers, but using two lot numbers seems to make this portion of the job much quicker, as the results are more easily recognized. I think using two lots helps avoid having to consider the element of random dispersion for this portion of the job. That element still exists, but at that point we're only looking at the calculated centres anyway, effectively letting us ignore that element. But I think the two lots will probably have different enough ignition/burn characteristics to make it less than ideal to use for the fine-tuning portion of the job. At that point I think you're better off focusing on a single lot so you can tweak just for its ignition/burn characteristics and get exit times tuned as best as possible.

I think slapping a Harrell onto any random barrel might actually be the root of the debate regarding whether or not tuners are even helpful. If it doesn't just happen to be in the right mass range for a given barrel then it will still have some effect, but that effect might seem more or less random. And I think the reason for that might be that if you aren't close to the right mass range for that barrel then what you're probably playing with as you change the setting is any/many of the harmonics above the fundamental. Each harmonic is responsible for less and less of the overall amplitude of barrel movement, but each harmonic step is also changing directions faster and faster. You might end up playing around with the 2nd or 3rd harmonic, or who knows which harmonic(s), and as you're twisting through the settings you're running across several different locations where the shots are exiting during different swing directions and different direction changes, too. Changing a Harrell by 25 clicks moves that mass out/in by 0.025" and can sometimes have a rather dramatic effect on the groups at the target. It's probably more than enough to put you into a different upswing or downwing portion of one of the many different harmonics that are present, or even have some shots leave during upswings and others during downswings of those harmonics. As you step through each harmonic each one contributes quite a bit less to the overall movement amplitude, but none of these are zero. The lower harmonics are the most important, as they're contributing the most movement.

(Whoa, ran out of room. I'll post the last paragraph in a minute or two here...)

 

[_Shorty]

cont'd...

As I say, I don't know that we're dealing with the fundamental for sure, but ideally that's what you'd want to deal with to have the most effect. I *think* that when you are in the right mass ballpark that the fundamental is what you are primarily affecting, but I'm not 100% on that. Different graphs from different people, both theoretical/simulated and from real-world measurements seem to indicate that it is the fundamental we are playing with when we are in the right ballpark, though. But I imagine when you are not pretty close to the right amount of mass that you can start dealing with higher harmonics, too. And in that case, you'd still see some kind of results, but the amplitude of changes seen would be smaller at each harmonic step. For example, and with made up frequency numbers just to illustrate, say the fundamental of the barrel were 5 Hz, and it moved 0.005" at that frequency. That would be more than enough for the required amount of just under 0.004" to make 50-yard compensation possible. The second harmonic of that would be 10 Hz, but the movement at that frequency might only be 0.0025", say. And perhaps at 20 Hz the movement there might only be 0.00125". Maybe we need to add enough mass to change that fundamental and move it down to 4 Hz to get ideal results, but perhaps the amount of mass in our Harrell that we slapped on moved it down to 3 Hz, and it isn't really helping much at all at that fundamental. But the second harmonic changed from 10 Hz down to 6 Hz as a result, and perhaps during some portion of its isolated swing movement in addition to the fundamental's movement we do see *some* improvement. Nothing close to ideal, but it does appear to help some, if we spin to just the right setting. But because it is changing directions much more often at that harmonic it becomes easier to hit a change in direction, and that's causing some unwanted randomness. Maybe shots are leaving during an upswing of that 3 Hz fundamental, and while that is not enough on its own, perhaps we luck out and some shots are also leaving during the upswing portion of the second harmonic, and sometimes this gets us close to the 4 Hz we want overall. So those shots actually receive a decent level of compensation and do well on target. Then some leave after that second harmonic's portion has started swinging downward, and the amount of compensation is worse, or hurtful. And on, and on, and on. So a tuner can help, and it can hurt, and it can do all kinds of random things. You have to get one that matches the barrel's added mass need in order to get the best results. An off-the-shelf one will likely only help if your barrel is pretty similar to whatever barrel was in mind when the tuner was designed.

 

[Mystic Precision]

We are not concerned about the bullets converging... we tune so their flight is parallel and stay in the tight cone.

When shooters shoot a clean target with all shots going into the Vbull (1/2 MOA), they are shooting very tight groups. And I believe a shooter just did that at Homestead at 900 with a 75-15V in a relay.. there was still some wind so driving was required.

Head out to a F class match and you can likely see how the targets plot (e targets bring an Ipad). No one is loading on site and everyone that is in the top 10 has loads tuned so their cone of accuracy stays tight from close to far.

My ideal tune is 1/4 MOA for vertical... and around 1/3 MOA for windage without the influence of wind

Some shoot tighter lateral then that. Anyone trying to win at high levels of competition will not have load vertical much over 1/3 moa... all the way to 1000yds

Jerry



Good load on the right... not as good on the left. Distance is 250yds and yes, the mirage was picking up right to left but I didn't bother to hold off. Heavier load means more powder in that ammo but otherwise, all other parameters the same.