Chronograph data and its effects

[Longstud]

Last week it was fairly decent weather and a few of us rimfire fans decided to get some dope and test some ammo lots as the start of the new season is upon us for the fair weather shooters!!

I have shot thousands of rounds in both centerfire and rimfire over a chronograph. I have very rarely seen these results with this many rounds! I have seen great SDs and ES numbers but never with entire boxes.
Just wondering what the rest of our crowd deduces from these numbers. I fired two groups of five that went into one hole at fifty yards with my Vudoo and hit 30 in a row on a1/4” KYL rack with my custom built semi.

Would like to hear civilized discussion without the useless bickering. If you don’t agree with someone just move on or add polite information you’ve found through your experiences. Thanks in advance

 

[grauhanen]

I don't expect that what follows should be controversial.

In terms of ES and SD for a box of .22LR match ammo, the lowest figures I've had were four boxes of RWS R50. The ES ranged from 17 fps to 21.5 fps with SD from 3.7 to 5.4 fps. This was with a couple of rifles. Other boxes of the same lots were not always quite so similar.

The thing with .22LR chronograph data is that good chrony results don't necessarily translate into equally good target results.

Box-to-box chronograph data can easily differ for ammo from the same lot at the same temperature. Chronograph users should think of .22LR ES and SD figures as part of a range of values possible in a lot/brick.

 

[Longstud]

The most accurate ammo I ever had shot in my first Vudoo was R50 but I never chronographed any. Was the R50 accurate in the rifles you tried it in? I’m beginning to think this is just another variable or rabbit hole. I will do some more playing!

 

[grauhanen]

The R50 was relatively accurate in the rifles I used but didn't produce the best results.

The Midas I shot last season had SD figures usually ranging from the low 5's to mid-7's with ES figures in the mid-20s to the 30's. Looking through my records today I found that I had a few boxes of M+ with SD numbers under 5 fps with ES in the 19 - 23 fps range. Most, of course, were not like these.

Last season I compared about ten different lots of Midas and three of R50. I have yet to see any .22LR match ammo lot that shot with consistently similar (alike) SD and ES values.

As an observation for readers in general, the chronograph can be a useful tool, but it doesn't replace results on targets when it comes to ammo selection.

 

[Chilly807]

My experience has been that ES and SD isn't as much of a factor at 50 yds as it is at 100 yds and beyond.

In fact, if I'm shooting at 50 with the chronograph set up, slower and faster shots very often don't hit the target where you would expect them to. Slower are often higher in the group, faster ones hit lower.

If that's positive compensation as a result of barrel harmonics, it makes sense. The rifle I'm using for most of this is an older Anschutz 1407.

Once I'm beyond 70-75 yds the effect of compensation, if that's what it is, is reduced. Slow shots do go low, fast shots hit high.

This is with ammo with decent ES/SD numbers to begin with, between 6 and probably 10 SD. Once you get above that, results are harder to interpret.
Otherwise, .22 ammo with high ES and SD numbers would be great at long range, and we know that's not the case.

 

[grauhanen]

In fact, if I'm shooting at 50 with the chronograph set up, slower and faster shots very often don't hit the target where you would expect them to. Slower are often higher in the group, faster ones hit lower.

If that's positive compensation as a result of barrel harmonics, it makes sense. The rifle I'm using for most of this is an older Anschutz 1407.

For readers in general, MV and POI often don't have a consistent relationship. As noted, some slower rounds may have a higher POI than faster ones, while some faster and slower ones strike higher or lower than MV predicts.*

(I will edit to add that, while MV/POI inconsistency occurs at 50 yards, it is much, much more obvious at 100. At further distances it would be even more obvious

It's not clear that MV/POI inconsistency is a result of positive compensation as a result of barrel harmonics. Why? Only some rounds from a box exhibit MV and POI mismatch. Most rounds will have a MV/POI relationship that is as would be expected. If positive compensation/barrel harmonics was the explanation it ought to apply to all rounds.

One explanation is that .22LR bullets with very similar MVs can experience barrel time variation -- that is, spend different amounts of time in the barrel -- with consequences for exit angles at the muzzle. While there may be published evidence for this occurring with centerfire ammo, there doesn't appear to be much, if any, with regard to .22LR.

Another explanation may be related to physical differences between bullets themselves. While .22LR bullets may appear to be identical, the shooter can't see even slight bullet imperfections. Bullet imperfection includes differences in form and shape, especially in the critical area of the bullet heel, as well impossible to identify differences in center of gravity. These typically can't be seen or measured without disassembling the cartridge or destroying it by firing it.
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*It's worth adding that POI irregularity can occur in the horizontal dimension as well, when some rounds strike further to the left or right than a normal dispersion pattern would predict. This may occur in conditions without wind or when air movement alone doesn't explain the POI.

 

[_Shorty]

Positive compensation is distance-specific. Another way to say that is you tune for one distance. Yet another way to say that is any given setup with a given ammo will shoot best at one distance, and shoot progressively worse the closer or further you go from that distance. The smaller the distance delta, the smaller the increase in dispersion. The larger the distance delta, the larger the increase in dispersion.

If you're finding slow shots hit higher at 50 yards that fast shots do this means if you add a certain amount of weight to the muzzle you will be able to get fast and slow shots to go through the same hole. Slow shots hit higher because the barrel is in an upswing, and currently that upswing is too fast to compensate for that distance. The launch angle continues to increase while the slower shot takes longer to travel down the barrel, and so it hits higher. Adding weight, such as a tuner, will slow the barrel down. And if you add just the right amount of weight it will slow it down just the right amount to change the launch angle just the right amount to compensate for bullet velocity differences, and you will then be "in tune."

Here's an interesting test to run. A modified version of my silhouette ammo search routine. Take whatever distance you have available and divide it into five reasonably spaced distances. Got 200 yards available? Try shooting at 40 yards, 80 yards, 120 yards, 160 yards, and 200 yards. Got 100 yards available? Try shooting at 40 yards, 55 yards, 70 yards, 85 yards, and 100 yards. Got five different ammo variants you can test? Shoot five five-shot groups at each distance, or ten five-shot groups if you really want to get good results, with each ammo variant and compare. You should see one best distance for each ammo variant. And it probably will not be the same distance for each variant. If you find one that shoots best at 120 yards it should shoot slightly worse at 80 and 160 yards, and slightly worse again at 40 and 200 yards. Whatever the best distance is, it should shoot worse with each distance step away from it, closer or further.

If you don't mind spending a lot of ammo you could progressively shoot in smaller distance increments around each last best result until you find the natural tuned distance for that gun and ammo variant. Shot best at 120 yards, and 160 yards was the next best? The natural tuned distance likely lies somewhere in between those. Shoot some at 130, 140, and 150 yards. Now maybe the two best results are at 130 and 140, so shoot 135 next. Eventually you'll find the distance with the best groups. If you move closer and closer than that best distance the groups will get worse. If you move further and further than that best distance the groups will also get worse.

You should be able to do the same with any ammo. In some cases you may find the best distance is fairly similar, and with others you may find it is quite different. It changes depending on the acceleration characteristics of each ammo variant and how that gets along with the barrel harmonics. The barrel tends to vibrate in the same fashion, but results differ because of differences in exit timing, how long shots take to ultimately exit the muzzle. And any time you see a difference in exit timing you should also see a difference in where the barrel is pointing at the time of bullet exit. And this is part of why different ammo gives different shooting results. Part of that answer is also how consistent the ammo is. You need consistent ammo that also agrees with the barrel and your target distance. And if you can use a tuner, that can also help.

 

[grauhanen]

The problem referred to above in posts #5 and #6 is of slower and faster rounds not having a POI that is consistent with their MV occurs only with some rounds. In other words, the majority of rounds go where MV would predict, with MV and POI having a consistent relationship. But some do not. While most rounds go where MV predicts, some faster rounds have a POI lower than slower ones and some slower ones have a POI higher than faster ones.

The problem of MV and POI mismatch or inconsistency occurs regularly and is not restricted to ammo make, grade, distance, or rifle. It occurs with match ammo lots at either 50 or 100 yards as any tracking of MV and POI will show. Once the trajectories of some rounds are skewed they can't be expected to self correct as they fly further down range.

Some lots may be better or worse than others when it comes to MV/POI consistency. But it's difficult to assess because MV/POI inconsistency is a matter of degree that requires a statistical evaluation that's not straightforward. (For example, two faster rounds that had a lower than expected POI may not have equally inconsistent POIs.)
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There is no such thing as .22LR ammo that's distance-specific. Using the problem referred to above, if a particular lot of .22LR match ammo was distance specific, all rounds should behave similarly, not only some of them. It's doesn't make sense that most rounds have POIs predicted by MVs while some don't. In fact, it's usual to see very good results mixed with the occasional errant round, either too high or too low (or, even in the absence of wind or when it's taken into account, too much to the left or too much to the right).

Of course two or more rifles/barrels can be excellent shooters at 50 with the same lot of ammo. But they may not shoot equally well at 100 with the very same ammo. Some barrels are better than others as distance increases.

The same is true for ammo. In the same barrel, some lots (even of the same variety (e.g. Center X or Midas +) are better than others as distance increases.

 

[_Shorty]

The problem referred to above in posts #5 and #6 is of slower and faster rounds not having a POI that is consistent with their MV occurs only with some rounds. In other words, the majority of rounds go where MV would predict, with MV and POI having a consistent relationship. But some do not. While most rounds go where MV predicts, some faster rounds have a POI lower than slower ones and some slower ones have a POI higher than faster ones.

The problem of MV and POI mismatch or inconsistency occurs regularly and is not restricted to ammo make, grade, distance, or rifle. It occurs with match ammo lots at either 50 or 100 yards as any tracking of MV and POI will show. Once the trajectories of some rounds are skewed they can't be expected to self correct as they fly further down range.

Some lots may be better or worse than others when it comes to MV/POI consistency. But it's difficult to assess because MV/POI inconsistency is a matter of degree that requires a statistical evaluation that's not straightforward. (For example, two faster rounds that had a lower than expected POI may not have equally inconsistent POIs.)
________________________________

There is no such thing as .22LR ammo that's distance-specific. Using the problem referred to above, if a particular lot of .22LR match ammo was distance specific, all rounds should behave similarly, not only some of them. It's doesn't make sense that most rounds have POIs predicted by MVs while some don't. In fact, it's usual to see very good results mixed with the occasional errant round, either too high or too low (or, even in the absence of wind or when it's taken into account, too much to the left or too much to the right).

Of course two or more rifles/barrels can be excellent shooters at 50 with the same lot of ammo. But they may not shoot equally well at 100 with the very same ammo. Some barrels are better than others as distance increases.

The same is true for ammo. In the same barrel, some lots (even of the same variety (e.g. Center X or Midas +) are better than others as distance increases.

Nobody said anything about ammo being distance-specific.

 

[Williwaw]

It's doesn't make sense that most rounds have POIs predicted by MVs while some don't.

I may be misunderstanding what you are saying here but that is exactly what happens on occasion and a rational explanation exists.

To clarify, if I am understanding Shorty correctly ... any rifle/ammo combination will perform optimally at a specific distance. Equally, any ammo/rifle/tuner combination will also perform optimally at one specific distance.

My only reservation in this regard is to say that I do not have a feel for the relationship between maximum possible barrel rise (which I presume would be achieved with a light tuner or no tuner) and optimal rate of barrel rise for PC (which I think requires more weight to slow the barrel down and therefore limit maximum barrel rise).

 

[_Shorty]

And in the case of ammo/rifle/tuner, what you are tuning is the optimal distance. Any given distance requires a certain speed in barrel movement in order to be "in tune." (And we also need to ensure we're riding an upswing.) The slower the movement, the closer the optimal distance. The faster the movement, the further the optimal distance. Using a tuner isn't dialing it in to "make it shoot better" just in general. It is dialing it in to shoot better at a specific distance. Spin the tuner in towards the 0 mark and you're moving that optimal distance away from you. Spin the tuner towards the 500 mark and you're moving that optimal distance towards you.

Whether or not a given ammo/rifle/tuner combination should allow you to dial it in for 50 yards depends on a few things. Probably the biggest factors being barrel length, barrel contour, and tuner weight. If you have an ammo/rifle/tuner combination you know to be in tune for 50 yards you could spin the tuner in towards the 0 mark until you can clearly see it has gone out of tune. And then you could incrementally move your target further away from you and find a distance where you're in tune again. Or you could spin it out further until you're clearly out of tune and then incrementally move your target towards you and find a distance where you're in tune again. You're not making the gun shoot worse by spinning the tuner in or out. You're simply moving that optimal target distance closer or further away from you. So if you keep your target at the same distance, and you start spinning the tuner, you're only making it shoot worse at that distance. And at the same time making it shoot better at another distance, which you could confirm by moving your target.

And this is why you can't use a tuner to make crappy ammo shoot great. You can still tune the optimal distance just like you can with the good ammo. But even when you have the optimal distance dialed in for the target distance that you're using, the ammo is still only going to be as consistent as that ammo is.

 

[Williwaw]

Again I may be misunderstanding but I would add some detail to your second paragraph Shorty. As I spin my tuner out for example, thereby moving the optimal distance nearer, I am not on a continuum but passing through a number of cycles which are composed of the upslope I am on, a peak, a downslope and a trough followed by the next upslope. Only the upslope positions represent potential optimum settings for some specific distance.

Thinking about it now it occurs to me that part of the merit/utility of the Hopewell Method is to scan the entire tuner range for a distance optimal setting. When I got my new Vudoo, now old, I was aware that the 22 inch barrel was on the short/stiff end of the spectrum. I shot a modified Hopewell with three different weights or weight combinations in order to choose the best weight and several prospective tuner setting ranges to investigate at that weight. It took a bit of ammo but since then I've gone through over 100K rounds with complete confidence that I'm working with near optimal tunes.

 

[_Shorty]

Yes, the goal is to have all shots leave during the upswing of the cycle. I'll steal a few of Varmint Al's diagrams that illustrate this. The first one is of a 24.75" reverse taper barrel without a tuner installed, typical of winning barrels that used to be pretty common in the benchrest world for a number of years not all that long ago. In the left image you can see that without a tuner on it the barrel is kind of straddling a peak node with these shots. The red dotted vertical line represents the exit time of a 1035 fps shot, and the blue dotted line is that of a 1075 fps shot. Then in the right image the curved line from left to right represents the muzzle projection at the target, red for the slow shot and blue for the fast shot. That is, anywhere along that line if the bullet exited at that time it would hit the target with that elevation. It is where the barrel is currently aimed, all along that curved line at that point in time. And where the dotted lines cross the curved line is where the shots actually left, so they hit the target at the elevation where each line meets its dotted line.



Straddling the peak node like that isn't ideal. This seems to result in a vertical delta between the shots of about 0.0764" or so, with the slow shot hitting higher. Kind of hard to measure with how low resolution the images are. Now we look at the same graphs with a 4.9-ounce weight installed at the muzzle.



You can see in this left image this has slowed the overall movement of the barrel down, and has moved both shot exits away from the peak node and now they're both exiting during the accelerating upswing. As a result, the right image shows their vertical delta is now fairly small in comparison to what it was without the weight installed. The delta now seems to be something like 0.0291" here. A nice improvement, but the slow shot is still hitting slightly higher, so we'd still like to slow the barrel down even more that the 4.9-ounce weight did here. The next one shows the same graphs, only this time with 8.6 ounces of weight installed at the muzzle.



The muzzle movement curve has an even gentler slope now, so it has been slowed down even more than with the last weight. Now the vertical delta between the two shots has shrunk to something like 0.0073" and seems fairly close to ideal now. We're very close to no difference at all. The next example jumps from 8.6 ounces of weight all the way to 16 ounces. A whole pound of weight added to the muzzle.



Now it has slowed it down a whole lot more, and the upwards swing doesn't really seem to be accelerating anymore. It hasn't quite reversed direction, but it has slowed enough that now the slow shot is hitting noticeably lower than the fast shot. It seems to be about 0.02" lower now compared to the fast shot. So 16 ounces would seem to be a lot more weight than you'd like on this barrel. The ideal would likely be pretty close to the previous 8.6-ounce weight. And so, ideally, your tuner would be close to that weight, just a hair under what might actually be ideal, and then you move the adjuster to dial it in just-so.

edit: And if shots actually leave with the barrel in a downswing then that means the fast shots are aimed higher than the slow shots. And since slow shots are already going to fall more by the time they reach the target you don't also want them to be aimed lower. This will do nothing but give you a huge vertical delta. Shots leaving during an upswing means the slow shots leave at a steeper angle and that compensates for their greater drop due to the lower velocity, reducing the vertical differences. Downswings make the vertical differences even worse.

 

[Longbow]

There was an entire cottage industry in the DCRA when Lee Enfileds were used as target rifles to achieve this at a set distance

 

[Williwaw]

There was an entire cottage industry in the DCRA when Lee Enfileds were used as target rifles to achieve this at a set distance

What is/was DCRA? Thanks

 

[Longbow]

Dominion Of Canada Rifle Association. It involved packing the fore ends of Lee Enflield Number 4 target rifles to achieve so many pounds of pressure in search of positive compensation. At the time matches were shot with issue ammunition. Apparently there was also a degree of witch craft and voduu involved in it. A long time DCRA shooter told me about it years ago when I was just a young pup. Each team had its own secret method

 

[Williwaw]

Thanks Longbow, that is very cool.

 

[_Shorty]

Yeah, I think the reason it wasn't as consistent as one would like is that with each shot the barrel moved against the pressure pad or whatever it was you were using, so sooner or later its behaviour would change. The amount of damping and/or preload that it was offering would change as things moved relative to one another, so it could go from noticeably helping to not doing much of any use, to actively fighting against the goal the more you shot. Could be great at the start of the day and garbage sometime later in the day. Or three weeks later. Or whatever. It likely wasn't a do once and forget about it situation.

 

[grauhanen]

Nobody said anything about ammo being distance-specific.

In another recent thread it was a key point you insisted was true. This is what you wrote: "I said if you find the distance that a given ammo shoots its best at then you will also find it will shoot worse at every other distance. This is 100% true."

I can understand if you've reconsidered.

I may be misunderstanding what you are saying here but that is exactly what happens on occasion and a rational explanation exists.

To clarify, if I am understanding Shorty correctly ... any rifle/ammo combination will perform optimally at a specific distance. Equally, any ammo/rifle/tuner combination will also perform optimally at one specific distance.

Post #6 above offers two explanations, only one of which seems plausible.

The idea that any ammo/rifle/tuner combination performs optimally at one specific distance is correct if positive compensation accurately explains how tuners work.

The idea that with no tuner involved any ammo and rifle will perform optimally at only one distance is not correct. Ammo is not distance-specific. Ammo that shoots very well at 100 will shoot very well at 50. But ammo that shoots very well at 50 may not shoot similarly at 100. Below is a brief explanation.

Since at least 1909 with the publication of Franklin Mann's book The Bullet's Flight From Powder to Target it's been known that there is a non-linear growth rate in group sizes as distance increases. In other words, groups get bigger or worse (MOA-wise) as distance grows.

In addition to gravity, a major cause of increasing group dispersion over distance is bullet imbalance. This is confirmed by Harold R. Vaughn in his 1998 book, Rifle Accuracy Facts.

It's worth noting that with .22LR bullet balance is a greater problem than with centerfire. This is because .22LR soft lead projectiles are likely to experience more imbalance than jacketed centerfire bullets.

Since group dispersion is non-linear, that is to say groups get bigger and bigger with distance (MOA-wise), no .22LR ammo can be a better performer at longer distances (MOA-wise) than at closer ones.

If groups get worse with distance, no ammo can be more optimal at a longer distance than a shorter one.

 

[Longbow]

The other thing he told me was that they always attempted to tune/achieve positive compensation at the longest distance shot in their matches. I guess with a tuner you could get a setting for each distance. Having said that I have no experience with tuners.