The conference rooms may not be filled to capacity here at NDIA, but there is more than enough data to keep this nerd happy for months. I’m scheduling most of these posts to keep you guys happy while Joe Grine and myself are off at the range having fun with machine guns and grenade launchers, but this one was just too interesting to hold off on…
ATK are the guys who run the Lake City armory. For those not in on the meaning of that statement, it means that they basically run the nation’s ammo plant. And as such, they want to be able to provide the best ammunition to our troops.
To meet that goal they wanted to see if short range testing (200 yards) would correlate well to long range results (1,000 yards). If short range testing indeed predicts long range performance then they can test ammo a lot faster and without taking up range time, which will in turn make the ammo better and produce it faster.
The basic assumption they made was the same one that fuels my ammunition consistency testing series: an increase in the deviation of the velocity of the ammunition will increase the spread of the impacts on the target.
Based on that assumption and some testing, they came to the same conclusion that I’ve come to, which is that the faster the round goes the less deviation there is in velocity. Slower rounds are inherently more inconsistent, and there’s nothing you can do about that.
Based on the initial testing they then went to the range with a bunch of experienced shooters and a bunch of rifles, and had them fire about 200 rounds each downrange. And the results were shocking.
ATK expected the ammunition to be more consistent as the velocity increased, but instead the overall accuracy remained more or less unchanged. And, in one instance, it even improved at lower velocity compared to higher velocity rounds.
So what does this mean? It means that the individual shooter and the way in which they interact with the firearm has much more to do with the overall accuracy of the shots than the ammunition or the gun. At least, that’s what I’m taking away from the presentation.
In short: quit blaming your ammo for your crappy shooting. Advice even I need some days.
“the faster the round goes the less deviation there is in velocity.”
Not necessarily. To a certain extent, if the variation is consistent (i.e. +/- 50 fps regardless of absolute velocity), then the faster ammo will have a slightly smaller % deviation. However there is no probable cause to suspect that the variation is independent of the total velocity.
My opinion is that different calibers/cartridges will have different “sweet spots” in velocity. Once you’re in that range, there should be little to no difference in performance within that sweet spot. However, if you push a given caliber to it’s absolute max velocity, you could exit that sweet spot and start to see induced variation from minor differences in cartridge capacity, peak pressure, etc. that add up to more variation. Same with going to a minimum velocity.
Higher velocity is generally preferred due to less bullet drop, however there is nothing inherent that should make lower velocity rounds less consistent. Just more difficult to dope out the range/drop estimate.
Again, my opinion after 25 years of engineering experience (although not in ballistics, I do use lots of statistics).
I would argue that quite a few loads tend to group better when loaded at a lower velocity. With the increased velocities you also have to increase the consistency of your component materials such as jacket thickness and core weight/position in order to maintain the same accuracy of a lower velocity load. Any small inconsistency will become more apparent quicker as the RPMs of the projectile will increase linearly with velocity. This in turn leads to greater centripetal force acting upon any inconsistencies within the projectile.
I want to award you one million internet bucks for using centripetal instead of “centrifical” force. Grammar and spelling nazis get all the fun, too much bad physics is allowed to slide.
On an ammo note: I like it when my ammo goes bang and puts holes in what it’s supposed too.
I am pretty sure you meant “centrifugal” not “centrifical”.
I am also pretty sure that centrifugal (inertia that comes from rotation and results in an outward force from the center of rotation) is the correct term anyway.
Centripetal force is when outer want to move to inner, centrifugal is inner wanting to move outer.
Just sayin’ and also not 100% sure.
Once again, I agree with caffeinated. Certain calibers often have velocity sweet spots. Just ask Tim Sundles of Buffalore bore or Hornady about their .308 Sniper ammo and superperformance match ammo. Accuracy involves a number of factors, but my 700 LTR loves 178 grain superperformance match .308, and shoots about 2 MOA or more with Federal American Eagle 150 grain. I’m confident that the best shooter in the world could not outshoot me with the same gun (on the bench or prone) with American Eagle if I get to chose my pet ammo.
Accuracy is a chain made of many links – good ammunition, clear scope, scope mount, shooting position, barrel harmonics, weather, competent shooter, clean barrel, coriolis effect, etc.
That’s great if ATK say so, but does not necessarily make it true. Also, the Lake City M855, M193, and MK 318 all shoot roughly 2 MOA, so they won’t challenge premium quality match ammo anytime soon, regardless of what ATK’s PowerPoint may say.
I have a Springfield M21 whose favorite load is 150 grain Federal Power-Shock. Shoots better at 300 yards and under than any load I’ve devised at 155, 168 or 175 grains. Bugs the living hell out of me actually, but it’s cheap at least! 🙂
“… In short: quit blaming your ammo for your crappy shooting. …
Ssssh. There’s about five hundred online gun forums that aren’t going to want to hear that news. 😉
What about RECOIL and how the shooter reacts to it? All things being equal, a higher velocity bullet will induce a bigger recoil, which will get some reaction from the shooter (flinching is one example), which will probably reduce the performance of the shooter and result in less consistent accuracy.
This comes as no surprise to anyone who has read through a Lyman’s reloading manual while looking for a pattern in all the “suggested most accurate” loads. You notice that a lot of the “suggested accurate loads” are at less than maximum velocities.
I’d venture that in all my reloading, very few loads I’ve developed have been most accurate at the max possible velocities. The amount of leade, bullet choice, rifling twist, etc all seem to make more difference than the exact choice of velocity or load.
Way back in the day, after I had qualified “expert” in pistol in the Air Force, I went out and bought me a Star PKM 9mm. That little sucker would put rounds all over the range except where I was aiming…unless I fed it Norma hollow point. Then it would shoot exactly where I was aiming it every time. Twitchy gun…
“an increase in the deviation of the velocity of the ammunition will increase the spread of the impacts on the target”.
I would have suspected the results to be all the same, regardless of the ammo.
No matter the expected deviation, as long as said deviation is consistent, groupings should be consistent. I’d be interested in seeing the test parameters and the data series they collected.
I assume grouping size data was their dependent variable, and then caliber, velocity, weight, etc. etc was their independent variables.
Anychance they can share the numbers?
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