Falconflyer
CGN Ultra frequent flyer
fascinating stuff!
Two-flats
- Thread starter _Shorty
- Start date
You don't get tight groups without the bullets converging. Again, this is literally impossible:
You think it is possible, as you've just repeated yourself on this point again. Frankly, there doesn't seem to be much point in discussing it any further if you can't accept that it is impossible. Have a good one.
Mystic Precision
CGN Ultra frequent flyer
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- Summerland, BC
Converge - "tend to meet at a point"... "to tend or move towards one point or another"
Yep, I got my understanding correct.
But hey, get out and visit an F class match with varying distances and see what the shooters and targets say (which if you haven't clued in, is scaled in MOA). I can assure you, our tuning does NOT converge at some distance... and the moa accuracy stays pretty constant to 1000yds
Jerry
PS for those new to the whole MOA, group size thingy... if you look at the table above, ALL targets have the same group size in MOA (0.3moa)... which is NOT the same as the physical distance between the bullets at varying distances. By definition, the impacts are physically further apart the further away the target is to the muzzle (no converging there) BUT have the same angular distance. This is the cone of accuracy LR shooters strive for.... and most prefer a smaller cone vs a larger cone.
YMMV
Yep, I got my understanding correct.
But hey, get out and visit an F class match with varying distances and see what the shooters and targets say (which if you haven't clued in, is scaled in MOA). I can assure you, our tuning does NOT converge at some distance... and the moa accuracy stays pretty constant to 1000yds
Jerry
PS for those new to the whole MOA, group size thingy... if you look at the table above, ALL targets have the same group size in MOA (0.3moa)... which is NOT the same as the physical distance between the bullets at varying distances. By definition, the impacts are physically further apart the further away the target is to the muzzle (no converging there) BUT have the same angular distance. This is the cone of accuracy LR shooters strive for.... and most prefer a smaller cone vs a larger cone.
YMMV
If you say so. Basic external ballistics theory disagrees with you, but what do ballisticians know about ballistics anyway? Bullets aren't lasers that fly straight where they're pointed. Bullets fly in parabolic arcs squeezed short by drag and the resulting loss of speed. And those arcs are defined by their velocity and departure angle. And this dictates that groups sampled at varying distances will have varying sizes. This directly contradicts your supposition that your groups will be the same size in MOA at all distances. A supposition which is physically impossible.
If you're shooting the same loads over and over while attempting to give them the same departure angles over and over, all those shots will diverge for a certain amount of distance after leaving the muzzle, and then converge around a given distance, after which point they will begin diverging again, and will continue diverging after that point. The whole idea behind tuning is to choose a convergence distance of your own so that you get the best results you can at that chosen distance. For some reason you have it in your head that bullets are like lasers flying in a straight line. That idea is completely wrong and has no basis in reality. Bullets don't fly straight like lasers, maintaining the same MOA as they go along in this supposed cone of accuracy. It simply does not work that way. And if you ever arrange a handful of the electronic targets that you have available for your use so that each shot goes through a few of them at different distances on its way out to 1000 yards and the final electronic target you will see for yourself that what I am describing to you is precisely what happens in reality. Groups will grow for a certain amount of distance downrange, will begin getting smaller again, will reach a point where they're smallest, and then will begin growing again and not stop growing. Whether you see all three of those stages depends on what distance your tune is good for. If you tune for the best groups at 500, and put targets at 250, 500, 750, and 1000, then you should see it do something like grow out to 250, shrink back down to their smallest at 500, grow again out to 750, and grow even more out to 1000.
Or you can just continue thinking you're right. I've already done tests like that, where one bullet passes through multiple targets at different distances, and seen for myself what happens at each distance. Maybe you need to see it with your own eyes to believe it. My guess is you'll just dismiss the whole idea because you think you already know. Which is fine. Doesn't matter to me if you want to learn or not. I've tried to help you learn, but it seems you're content with what you already hold to be true regardless of whether or not it is actually true, so you can have that. Horse, water, and such.
The question was related to the familiar idea that barrels that are slimmer are more responsive (or to put it another way, more reactive) to the use of a tuner than those with substantial diameters.
(For general readers who may not be aware, tuners do their "thing" more effectively on barrels that are not too heavy or stiff. It's a key reason why RFBR shooters use barrels that are typically about 24"- 26" long and about .800" - .900" in diameter -- a "Goldilocks range". They don't want barrels that are too "stiff" yet not too slim. Stiffness appears to be a product of length and diameter. To illustrate, a shorter barrel is more challenging to tune than a longer one of the same diameter.)
The question of how tuners work -- do their thing -- is a key to whether this is a concern. If the statement refers only to centerfire, perhaps it also involves the question whether rimfire and centerfire tuners work the same way.
In rimfire, if tuners work because they achieve positive compensation (outlined, for example, in Varmint Al webpages), tuning is all about bullets converging. The idea is that a rimfire rifle that's tuned at 50 yards will have faster and slower bullets converging closer at the POA. Slower bullets have a higher exit or launch or shooting angle than faster ones. The result is that faster and slower bullets arrive closer to the same POI (converging) than would otherwise be the case due to the effects of MV and gravity only. Of course this means that tuners must be readjusted for different distances, that the same tuner setting is not equally effective for all distances.
Although it's not clear what parallel flight means, perhaps the idea is achieved by tuning the barrel so that the muzzle doesn't move because it has a node, a place where the wave motion doesn't move the exit angle of the muzzle and the rounds leaving it. Perhaps this is what Bill Calfee meant by a "stopped muzzle". A stopped or non-moving -- non-vibrating if you will -- muzzle will send bullets to their destination at the same exit angle with the result that only MV (with no wind and with perfectly formed, symmetrical bullets) determines the POI. It may, in effect, take barrel vibrations out of the equation. Is this what "parallel flight" is about?
Of course, with a barrel with a node at the muzzle -- no changing launch angle -- bullets with different MVs can't be expected to have identical (parallel?) trajectories. With positive compensation, bullets with different MVs can be expected to have more similar trajectories -- but only to a certain distance. Once past that distance, the paths will diverge.
Do one or the other adequately explains how tuners work?
As a point of reference, under perfect circumstances, at 50 yards with the same launch angle, each difference in MV of 10 fps between two rounds results in about 0.07" of vertical; at 100 each 10 fps difference means 0.27" of vertical; at 200 every 10 fps difference in MV results in about 1" of vertical. When the MV variation is 10 fps, at 50 yards the difference in POI has only a little room for improvement with a tuner. A BR shooter with a tuned rifle shooting a good lot of ammo with a small ES doesn't expect or need much improvement from his tuner, but even a little bit helps.
Here is a plot of the trajectories of 0.284 Berger 180-grain Hybrid Target bullets with a 1000-yard zero, one that was 2840 fps, and one that was 2860 fps, same as the example I gave before.
Somewhere near the 560-yard mark the 2840 fps bullet is right about 1.5" higher than the 2860 fps bullet, the point of maximum delta between the two. Before and after that mark the difference is less. This is part of why you cannot have the same size groups at all intervals between you and the 1000-yard target. Why isn't max delta at half distance? Why is it at 560 yards and not 500 yards? Drag. They're slowing down. If you took the same shots with the air removed from the equation they wouldn't have a 1000-yard zero because they wouldn't be slowing down, and they would then exhibit max delta at half distance, whatever that distance would end up being. Or if you compensated your aim so the no-air zero was still at 1000 yards then the point of max delta would indeed be the halfway point at 500 yards.
I am pretty much convinced that Bill Calfee didn't really understand what was going on when he made that statement, because of how he describes what he sees on target when he has what he calls a stopped muzzle. From what he describes he sees in his shooting results when his muzzle is "stopped" it sounds like he's actually just got his positive compensation pretty much bang on. He is a great gunsmith and knows how to get great results, but that doesn't necessarily mean he understands everything that is going on. It's like you say, if the muzzle were actually stopped then MV would dictate vertical stringing. But he considers the muzzle stopped when he sees no vertical in his targets. But when you see no vertical in your targets that barrel is in an upswing with a very nice rate. Bill thinks he's got it stopped at either the top or bottom of the swing when shots exit, but he does not. If he did, he'd have a ton of vertical. And if I remember correctly, he was talking about how he knows he doesn't have enough weight when he still has vertical. He knows enough about the concept to reach the desired end goal, and whether he's undershooting or overshooting that goal, but I don't think he really understands what's going on completely. Or he's just goofing on us. He likes to write in a purposely murky way to try and make out like he's a dumb guy for some reason, so it isn't always easy to tell if he is relaying exactly what he really means. He's a character. But from how he words that discussion, it sounds like he doesn't really know what's going, 100%, but does know how to go about removing vertical. Like I say, it's just that his description of how it removes vertical wouldn't actually remove vertical. He seems to have positive compensation dialled in, bullets leaving during a just-right upswing, while thinking he's got something else dialled in, bullets leaving at the top or bottom node of barrel movement. I don't remember off the top of my head if he said he knew whether it was the top one or bottom one, or if he was after one or the other, or if either one was fine. In the end, either of those situations wouldn't do what he thought anyway.
Somewhere near the 560-yard mark the 2840 fps bullet is right about 1.5" higher than the 2860 fps bullet, the point of maximum delta between the two. Before and after that mark the difference is less. This is part of why you cannot have the same size groups at all intervals between you and the 1000-yard target. Why isn't max delta at half distance? Why is it at 560 yards and not 500 yards? Drag. They're slowing down. If you took the same shots with the air removed from the equation they wouldn't have a 1000-yard zero because they wouldn't be slowing down, and they would then exhibit max delta at half distance, whatever that distance would end up being. Or if you compensated your aim so the no-air zero was still at 1000 yards then the point of max delta would indeed be the halfway point at 500 yards.
I am pretty much convinced that Bill Calfee didn't really understand what was going on when he made that statement, because of how he describes what he sees on target when he has what he calls a stopped muzzle. From what he describes he sees in his shooting results when his muzzle is "stopped" it sounds like he's actually just got his positive compensation pretty much bang on. He is a great gunsmith and knows how to get great results, but that doesn't necessarily mean he understands everything that is going on. It's like you say, if the muzzle were actually stopped then MV would dictate vertical stringing. But he considers the muzzle stopped when he sees no vertical in his targets. But when you see no vertical in your targets that barrel is in an upswing with a very nice rate. Bill thinks he's got it stopped at either the top or bottom of the swing when shots exit, but he does not. If he did, he'd have a ton of vertical. And if I remember correctly, he was talking about how he knows he doesn't have enough weight when he still has vertical. He knows enough about the concept to reach the desired end goal, and whether he's undershooting or overshooting that goal, but I don't think he really understands what's going on completely. Or he's just goofing on us. He likes to write in a purposely murky way to try and make out like he's a dumb guy for some reason, so it isn't always easy to tell if he is relaying exactly what he really means. He's a character. But from how he words that discussion, it sounds like he doesn't really know what's going, 100%, but does know how to go about removing vertical. Like I say, it's just that his description of how it removes vertical wouldn't actually remove vertical. He seems to have positive compensation dialled in, bullets leaving during a just-right upswing, while thinking he's got something else dialled in, bullets leaving at the top or bottom node of barrel movement. I don't remember off the top of my head if he said he knew whether it was the top one or bottom one, or if he was after one or the other, or if either one was fine. In the end, either of those situations wouldn't do what he thought anyway.
This is as good a characterization as I've seen of Calfee's words.
Leuchtkafer
Member
Haha, that's funny saying you had it cut out for the scope! First thing I thought when I saw it was whether the bore got distorted from the machining, have you tried slugging it to see if anything feels off?
I'm seeing something different from Bill Calfee, he describes a stopped muzzle as having the exact centre of the parallel node at the crown, the muzzle does not swing up and down, the tuner takes on that partial cycle in the barrel's place. Vertical on target falls to the consistency of the ammo, and he says with the very best lots of ammo available, that leaves about 0.15" at 50 yards. He may not be the best at communicating it, but I think he understands the concept of what he is doing very well.
I'm seeing something different from Bill Calfee, he describes a stopped muzzle as having the exact centre of the parallel node at the crown, the muzzle does not swing up and down, the tuner takes on that partial cycle in the barrel's place. Vertical on target falls to the consistency of the ammo, and he says with the very best lots of ammo available, that leaves about 0.15" at 50 yards. He may not be the best at communicating it, but I think he understands the concept of what he is doing very well.
One of my worries that came later on regarding this barrel, after having to deal some more with the company to get some things ironed out, was whether or not they'd actually been truthful about their manufacturing. I was told it would be a cut-rifled barrel, and that it would be hand-lapped after the machining. I'm not sure if either of those were true, and in the case of the latter it would mean having to cut the chamber and muzzle afterwards, too. I wish I knew for certain what went on with it, but I don't. If that's actually the case, and it was cut-rifled, that should do away with most of the worry about the bore becoming distorted with the machining done to the outside after the fact. I believe the worry of distorting the bore is most deserved when dealing with a button-rifled barrel, due to the amount of stress put into the material from the button going through it. This is also something that pops up when you go to through a muzzle for a muzzle brake or suppressor. I've seen video of someone checking barrels with gauge pins before and after threading the muzzle, and pins that would previously not go into the bore before the job would slip right in after the job. But I'm sure this was a button-rifled barrel in that example. With the cut-rifling process not inducing those kinds of stresses in the material one would think that removing any material from the outside wouldn't have any or much effect on the bore inside. That being said, this barrel shoots fairly fast compared to some others I have tested, and I'm relatively confident the bore isn't too bad. I'm not necessarily convinced it is a superb bore, and I still have doubts about who made it and how it was made, but it seems like it is at least a decent bore. I would think, as it sounds you do, that if I slugged it and the bore did have corresponding flat spots in it due to the outside machining that the bullets would come out with some unusual shape that would likely be obvious. I have slugged it a few times to see if I could feel any tighter or looser spots along its length, and I don't think I could detect anything doing that by hand, but I don't recall seeing anything odd about the bullets after going through. I think it might be alright. But as I say, I'm not yet convinced one way or the other about its overall bore quality. I don't really know if it is a good barrel. I'm hoping the upcoming testing with the Tenex will reveal a lot more of its characteristics, which it should. Probably wouldn't be a bad idea to slug it again a few times and look specifically for any oddness in the bullet shape from the flat spots, as I don't think I really looked for that before. I only recall not noticing anything remarkable at the time, but I don't think I was looking for anything along those lines then, either. It does shoot relatively fast. My average velocities seem to be roughly 40 fps faster than what Eley gets in their four test barrel average that's listed on the boxes. That might mean it is slightly tighter than average, I think.
Honestly, it has been quite a while since I read any of Calfee's writing on the subject, so I very well could be mistaken about what he was saying exactly, for sure. But I think something important to note would be that even in the case that you now describe the angle that the muzzle would be pointing would still be changing. You'd just have moved what I would loosely call a pivot point (bending point?) from further back along the barrel to the area of the muzzle instead. It would still have some amount of departure angle change from what it was doing. Perhaps a smaller amount. If we're looking at it as though it were a standing wave with the muzzle at the node then what's happening behind the muzzle is still going to be affecting where the muzzle is pointing. You'd be minimizing the displacement of the muzzle in space, but the angle leading to it, the angle that it is pointing at, would still be changing. I would imagine this could be quite a change in influence compared to actual muzzle displacement, assuming that's what's actually going on, that is. It isn't necessarily what's actually going on, but it might be. I'm inclined to think that isn't what's going on, though.
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Calfee has been seen as everything from a paragon of rimfire BR rifle building knowledge and experience to little more than a quack deserving little, if any attention. And all of this in less than two decades. He is probably best described as being somewhere between the extremes. As Leuchtkafer (Rabid?) points out, Calfee is not a great communicator. That's always a problem, especially in discussions of technically-related issues, as it diminishes rather than strengthens an idea or view.
His personality, including a propensity to claim credit where it's place was not always clear (he claims to have invented the muzzle device -- his term for a tuner), rub many the wrong way. When the Varmint Al webpages, and particularly the work of Geoffrey Kolbe, elaborated on the positive compensation explanation for tuners came out almost ten years ago, Calfee's theory of the "stopped muzzle" became viewed as plainly wrong.
Calfee's disagreements with other rifle builders and shooters, many of them purged from the various forums on which they first appeared, haven't for one reason or another generally gone in his favour -- at least in the views of his critics, now probably a majority of RFBR shooters and followers. For them Calfee has become a pariah.
Curiously, some of those RFBR shooters who criticize Calfee, insist that their tuners work without readjustment at both 50 and 100 yards. Of course, the positive compensation theory that Kolbe used to attack Calfee's "stopped muzzle" theory requires tuner readjustment with a change of distance because bullets with differing MVs can only converge once at a certain distance during their flight. With a growing body of PRS shooters insisting that tuners work at all distances without readjustment, it seems the explanation for how tuners work remains without a universally accepted consensus.
His personality, including a propensity to claim credit where it's place was not always clear (he claims to have invented the muzzle device -- his term for a tuner), rub many the wrong way. When the Varmint Al webpages, and particularly the work of Geoffrey Kolbe, elaborated on the positive compensation explanation for tuners came out almost ten years ago, Calfee's theory of the "stopped muzzle" became viewed as plainly wrong.
Calfee's disagreements with other rifle builders and shooters, many of them purged from the various forums on which they first appeared, haven't for one reason or another generally gone in his favour -- at least in the views of his critics, now probably a majority of RFBR shooters and followers. For them Calfee has become a pariah.
Curiously, some of those RFBR shooters who criticize Calfee, insist that their tuners work without readjustment at both 50 and 100 yards. Of course, the positive compensation theory that Kolbe used to attack Calfee's "stopped muzzle" theory requires tuner readjustment with a change of distance because bullets with differing MVs can only converge once at a certain distance during their flight. With a growing body of PRS shooters insisting that tuners work at all distances without readjustment, it seems the explanation for how tuners work remains without a universally accepted consensus.
Shorty, with regard to looking for evidence that machining the flats caused issues within the bore, you wrote "if I slugged it and the bore did have corresponding flat spots in it due to the outside machining that the bullets would come out with some unusual shape that would likely be obvious."
Perhaps you wouldn't be slugging the entire length of the bore. What would you be looking for on the slugs?
Perhaps you wouldn't be slugging the entire length of the bore. What would you be looking for on the slugs?
Yeah, as I mentioned before, Calfee is a character. Kolbe's measurements are something I've referred to quite a bit. For 50 m he worked out that the muzzle needs to have an upswing of around 6 MOA per millisecond to give near ideal positive compensation, and repeating the work myself to see if I understood him correctly yielded a value of 5.97 MOA per millisecond for the velocity range he was talking about. I took that to mean that I had followed along with what he was saying. Having since tried the same calculation with different values for velocity it would appear that this is also affected by drag, as I don't get the same compensation value for shots with velocities of 1035/1075 fps as he did for shots with velocities of 1010/1060 fps. I took this to mean that you'll have to retune every time you switch lots of ammo, in addition to when you switch distances.
And as far as tuning for different distances go, I don't see how this is anything but a must. As you mentioned again, convergence at 50 yards means no convergence at 100 yards. In fact, the amount of compensation required for 100 yards is nearly double that's required for 50 yards.
To repeat again, tuning for one distance induces more vertical at other distances, so PRS shooters thinking their tune is good for any distance are fooling themselves. You can select a distance that would be a good compromise for the other distances, but you can only tune for one distance. I'll post this table from the first page again that shows the amount of induced vertical at different distances with different tuning distances.
If you refer to the small table for the 1035/1075 values that I've been using you can see that the compensation required for 50 yards is 5.146875 MOA per millisecond. That converts to 0.001497164175 radians per millisecond, which in turn converts to 0.23828107907134946 Hz. Then, 100 yards requires 10.03125 MOA per millisecond, which is 0.00291797025 radians per millisecond, which is 0.46440938908259366 Hz. So even though we're talking about relatively slow vibrations here, we are still talking about quite a difference required to tune for 50 yards versus 100 yards. I don't know how the amounts of compensation required for centrefire might compare. I think I'll do up a table just to satisfy my own curiosity, but all that will be different there is the amount of difference involved. It is still going to be different for different distances, as that's just how it works.
Hmm, perhaps I was a bit foggy at the time I wrote that. The flats are removed material, and so that should make the top and bottom of the bore actually get larger if it were to do anything. Perhaps my barrel shooting relatively fast is an indication that it was indeed cut-rifled. I would think if the bore were affected that the seal would be horrible as it rotated through the larger portions at the top and bottom if it had grown at the top and bottom due to the flats. And perhaps there wouldn't actually be any visible evidence on the slugs in that case, especially considering that the breech and muzzle ends are round anyway. So it would start off with typical lands and grooves, and if the portion with the flats had changed they'd just be slightly larger there. I don't think I thought that one through very well, hehe. I guess you could air gauge it to see how uniform things are along its length. But, again, perhaps the fast nature of it indicates that it is a fairly decent bore. I'd think it would be slower due to gas escaping past the bullet if it had grown due to the flats.
And as far as tuning for different distances go, I don't see how this is anything but a must. As you mentioned again, convergence at 50 yards means no convergence at 100 yards. In fact, the amount of compensation required for 100 yards is nearly double that's required for 50 yards.
To repeat again, tuning for one distance induces more vertical at other distances, so PRS shooters thinking their tune is good for any distance are fooling themselves. You can select a distance that would be a good compromise for the other distances, but you can only tune for one distance. I'll post this table from the first page again that shows the amount of induced vertical at different distances with different tuning distances.
If you refer to the small table for the 1035/1075 values that I've been using you can see that the compensation required for 50 yards is 5.146875 MOA per millisecond. That converts to 0.001497164175 radians per millisecond, which in turn converts to 0.23828107907134946 Hz. Then, 100 yards requires 10.03125 MOA per millisecond, which is 0.00291797025 radians per millisecond, which is 0.46440938908259366 Hz. So even though we're talking about relatively slow vibrations here, we are still talking about quite a difference required to tune for 50 yards versus 100 yards. I don't know how the amounts of compensation required for centrefire might compare. I think I'll do up a table just to satisfy my own curiosity, but all that will be different there is the amount of difference involved. It is still going to be different for different distances, as that's just how it works.
Hmm, perhaps I was a bit foggy at the time I wrote that. The flats are removed material, and so that should make the top and bottom of the bore actually get larger if it were to do anything. Perhaps my barrel shooting relatively fast is an indication that it was indeed cut-rifled. I would think if the bore were affected that the seal would be horrible as it rotated through the larger portions at the top and bottom if it had grown at the top and bottom due to the flats. And perhaps there wouldn't actually be any visible evidence on the slugs in that case, especially considering that the breech and muzzle ends are round anyway. So it would start off with typical lands and grooves, and if the portion with the flats had changed they'd just be slightly larger there. I don't think I thought that one through very well, hehe. I guess you could air gauge it to see how uniform things are along its length. But, again, perhaps the fast nature of it indicates that it is a fairly decent bore. I'd think it would be slower due to gas escaping past the bullet if it had grown due to the flats.
As a general observation for readers, the "speed" of a barrel -- that is, whether it tends to shoot an ammo faster or slower -- may well be related to bore diameter in that tighter bores may shoot faster than less tight ones. It's also worth noting, however, that bore characteristics may play an important role in determining how fast or slow a barrel may be. Bore smoothness, for example, may be relevant to how fast it allows rounds to pass through. Of course this, as well as bore diameter variation through the length of the barrel, which may also be important here, is not easy to measure.
Another significant factor is the ammo itself. Some ammos are faster (or slower) than their "advertised" speed, the speed that's printed on a box, derived from a lot number (as in the case of Lapua) or offered as a nominal MV by the manufacturer.
For example, I have some Eley ammo that's rated 1062 fps on the box. In two different rifles with 27" barrels, one of which shoots "slower" than the other, the ammo was still faster than the box rating. In another example, two lots of RWS Special Match ammo, which has a factory rated MV of 330 meters/second (1083 fps) regularly shot faster. The many different lots of Lapua tested over the past three years usually performed closer to MVs based on lot numbers -- but all are slower on average, regardless of which 27" barrel rifle used, even with a 26" barrel.
Although these examples are not conclusive by any means, it's possible that some brands of ammo may often be faster or slower than might be expected.
Another significant factor is the ammo itself. Some ammos are faster (or slower) than their "advertised" speed, the speed that's printed on a box, derived from a lot number (as in the case of Lapua) or offered as a nominal MV by the manufacturer.
For example, I have some Eley ammo that's rated 1062 fps on the box. In two different rifles with 27" barrels, one of which shoots "slower" than the other, the ammo was still faster than the box rating. In another example, two lots of RWS Special Match ammo, which has a factory rated MV of 330 meters/second (1083 fps) regularly shot faster. The many different lots of Lapua tested over the past three years usually performed closer to MVs based on lot numbers -- but all are slower on average, regardless of which 27" barrel rifle used, even with a 26" barrel.
Although these examples are not conclusive by any means, it's possible that some brands of ammo may often be faster or slower than might be expected.
So I downloaded Gordon's Reloading Tool in order to get bullet exit times for a centrefire load, and it fired up with a 6.5 Creedmoor load by default that used a 120-grain Sierra HBT Match King bullet at 2980 fps, so this is what I used at my example just to make things easy, and adjusted power slightly to get MV values 15 fps faster/slower to give a 30 fps ES. Then I calculated how much compensation was needed to tune at 100-yard intervals out to 1000 yards, as well as what the various bullet drops would be at those distances for those two speeds. So as a result, I've got muzzle upswing rates for getting optimal positive compensation for 100-1000 yards and also how much vertical is induced at each 100-yard interval when tuned for each 100-yard interval, similar to the charts I made for 1035/1075 fps rimfire earlier. Here's the positive compensation muzzle upswing rate chart, which also includes the frequency this time. The rad/s value is just an intermediate value I needed for the frequency calculator.
It is interesting to compare this round's 100-yard compensation requirement of 2.157895 MOA/ms to the rimfire round's 10.03125 MOA/ms. Quite the difference. And there's quite the range here going from 100 yards out to 1000 yards. And here's the induced vertical chart. As before, the ivalues are in inches.
And as we saw with the rimfire chart, you get a range of induced vertical that rises until you get roughly to the halfway point between you and the target, and then begins falling again until you reach the tuned distance, and after you go beyond the tuned distance the amount of induced vertical just begins climbing and continues to do so from that point on. So the lesson is the same here with centrefire as it is with rimfire, which is that you either tune for every distance you're shooting or you choose a compromise distance that gives an acceptable amount of induced vertical at the other distances. The example here is the 6.5 Creedmoor load that I mentioned, but the same is going to hold true for any other calibre/load you choose. The actual numbers you get with a different calibre/load will change, but the same pattern will exist. In this case, the 6.5 Creedmoor load with an average MV of 2980 fps and an ES of 30 fps can result in up to 8.84" of induced vertical out at 1000 yards if you did your best to tune it at 100 yards. Jerry mentioned doing this tuning at 300 yards when that's all your practice space allows, and if you look at the 300 tuned column you can see that this would entail accepting up to 7.78" of induced vertical out at 1000 yards with this 6.5 Creedmoor load example. Obviously not ideal. This time I've also included a line for the average induced vertical for each tuned distance so you can see where it would make the most sense to tune if you were to tune at just one distance in order to get the least amount of induced vertical at all distances. The best compromise, in other words. And in this case that would be tuning at 700 yards. I also updated the rimfire chart to include the same average induced line.
It is interesting to compare this round's 100-yard compensation requirement of 2.157895 MOA/ms to the rimfire round's 10.03125 MOA/ms. Quite the difference. And there's quite the range here going from 100 yards out to 1000 yards. And here's the induced vertical chart. As before, the ivalues are in inches.
And as we saw with the rimfire chart, you get a range of induced vertical that rises until you get roughly to the halfway point between you and the target, and then begins falling again until you reach the tuned distance, and after you go beyond the tuned distance the amount of induced vertical just begins climbing and continues to do so from that point on. So the lesson is the same here with centrefire as it is with rimfire, which is that you either tune for every distance you're shooting or you choose a compromise distance that gives an acceptable amount of induced vertical at the other distances. The example here is the 6.5 Creedmoor load that I mentioned, but the same is going to hold true for any other calibre/load you choose. The actual numbers you get with a different calibre/load will change, but the same pattern will exist. In this case, the 6.5 Creedmoor load with an average MV of 2980 fps and an ES of 30 fps can result in up to 8.84" of induced vertical out at 1000 yards if you did your best to tune it at 100 yards. Jerry mentioned doing this tuning at 300 yards when that's all your practice space allows, and if you look at the 300 tuned column you can see that this would entail accepting up to 7.78" of induced vertical out at 1000 yards with this 6.5 Creedmoor load example. Obviously not ideal. This time I've also included a line for the average induced vertical for each tuned distance so you can see where it would make the most sense to tune if you were to tune at just one distance in order to get the least amount of induced vertical at all distances. The best compromise, in other words. And in this case that would be tuning at 700 yards. I also updated the rimfire chart to include the same average induced line.
Rate up muzzle upswing for positive compensation at that distance.
edit: Perhaps it is worth mentioning that in Kolbe's tests he measured that it would take about a 375 fps difference in MV to equal 1 ms of exit time difference, so here I am using whatever the rimfire MV difference is /375 in order to get the difference in exit time in ms, so 40/375 in the case of the 1035 fps and 1075 fps shots, or 0.10667 ms. And in the case of the 6.5 Creedmoor example, the GRT app tells me that there is a 0.019 ms difference in exit time for the 2965 fps vs 2995 fps shots. So, the difference in required launch angle divided by the number of ms that pass between those shots exiting gives you the MOA/ms of muzzle upswing required for positive compensation.
edit2: Interesting. Switching to MOA instead of inches seems to move the optimal single tuning distance for shooting within 1000 yards to somewhere between 500 and 600 yards. I wonder if this is related somehow to the 560-yard trajectory max delta we saw with the .284 1000-yard shots example. Might simply be an inverse of that delta in some way. Perhaps you tune for that point, and you're reducing the delta at all other points as much as possible as a result.
edit3: Extended that further to include scenarios where you'd exclude shorter distances. This seems to also moves the optimal single tuning distance further out every time you exclude a shorter distance.
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Honestly with centerfire, I'd just load carefully for a minimum ES and "tune" for a consistent launch angle so that vertical is mitigated at all distances, but maybe I'm just crazy
Or maybe you didn't understand what I just finished saying. If you don't understand something, ask questions. Dismissing something when you don't understand it doesn't lead to learning anything, but asking questions can. If you did understand what I just finished saying, well, you wouldn't be dismissing it. Unless you were actually crazy.
Leuchtkafer
Member
Or maybe you didn't understand what I just finished saying. If you don't understand something, ask questions. Dismissing something when you don't understand it doesn't lead to learning anything, but asking questions can. If you did understand what I just finished saying, well, you wouldn't be dismissing it. Unless you were actually crazy.
Well you know the saying that genius borders on insanity, it's quite possible I skew more towards the insane side hehehe. I understand all the theory behind the positive compensation approach, you've got it all laid out well showing that to achieve such and such, muzzle must move at "X" rate. Great. What I find lacking though, is nobody has a solid methodology of how to actually go out and accomplish inducing the required conditions of muzzle movement. About the sum of it is "go out and try a bunch of things and hope you get lucky", yeah? Like with this two flats barrel, very interesting work modelling out the vibration pattern, but where is the modelling to get it performing in the desired manner? Has anyone done some work to show something like, if using ammo with "X" ES, add this much weight at this distance beyond the muzzle and you should be in the ballpark of the actual real world setting required? I'm not trying to be a dink here, just highlighting a gap I see in applying the theory to the real world. I observe a lot of people floundering about trying to make it work, it'd be nice if the tuning process could be solidified into something that is more concrete and less "trial and error".
As an aside, see built into the name of the theory is "compensation". What is being compensated for? A deficiency. A deficiency in what? The ammo. Ah. See, I like to get to the root cause of things and fix that if I can rather than applying a band-aid fix. Much has been attempted with rimfire rifles in an effort to somehow counteract a flaw in the system. After decades, there's only so much that can/has be done with this approach. How's my logic on this: If the ammo could be made with near perfect consistency, is there anything to really "compensate" for? Would you want to have a muzzle that moves significantly or a muzzle that is as still as possible, if given this ammo?
At the end of the day we're still stuck with factory ammo and all it's inherent flaws, so one is left with the choice of either trying to compensate for it or accepting it for what it is. Different strokes for different folks. When you see people saying they don't tune for different distances, take it that they're just setting their rifle for a consistent launch angle regardless of velocity and just accepting the vertical that will result. The games are designed around that with larger targets at greater distances so one can score their hits. All that matters is that we're enjoying what we're doing, some will find your pursuits more frustrating than enjoyable and that's fine, they can do something else that they find more enjoyable. You've taken a keen interest in what you're doing and that's a good thing. Who knows, maybe you'll be the one to really nail down positive compensation and how to achieve it with different barrel/ammo variables? That'd be pretty groundbreaking for the community and a most notable achievement. I'd be happy to see you do it and I wish you all the best in your efforts.
