Accuracy & Precision vs. Bullet Jump

Less of a question than an observation......thinking out loud. Was recently following a thread on another forum where controversy was complaint a guy had that revolved around a bullet offered for .243 Win and 6mm Rem. One caliber with twist of 10:1, the other 9:1. Complainer was an experienced reloader whose complaint was the online seller's website didn't mention twist rate for the bullet. Wrath from the others was if he was experienced, he should have known the difference.

As someone who in the past has mostly dropped factor ammo in guns and shot em.......someone who is now getting up to speed on the technical stuff that goes on behind the scenes so to speak, on the surface the difference between the two seems negligible. That they are different and need to be is new to me is all. I'm finding out all kinds of helpful stuff.

@Howa 9700 - ******** do exist on the internet. No speculation, the experiment set is null, I know, because I’m here... so I have no surprise when someone notices our existence online.

In defense of those chastising that poster, in general, yes, the science behind bullet stabilization is well understood: if you know the length and weight of the projectile and the velocity to which it can be driven, a few common formulas, even a few common online calculators, will determine your stability, or lack thereof - and an experienced rifle reloader and shooter should be familiar with these.

In defense of the poster, there are a LOT of generalizations flying around which don’t apply to all bullets, and a lot of online ******** will ignore the influence of LENGTH on stability. An example of this: the 22 caliber 77 Sierra Matchking is a stubby little bullet designed to fit into AR-15 magazines. Such, it is much easier to stabilize than many other bullets in its weight class, for example, the 75 A-Max/ELD-M. There also exist round nosed bullets in many calibers which are very short for their weight, and much easier to stabilize than a long ogive spitzer. So it’s nice for us reloaders and shooters when manufacturers suggest a twist rate for a given bullet, or when other reloaders and shooters can reference unique profiles which buck conventional standards.

In defense of the manufacturer in that case - it’s somewhat foolish when us reloaders and shooters are comforted by recommended barrel twist specs, because it’s really the RPM’s which matter, not the twist alone. A 6mm Creedmoor will push a bullet much faster than will a 6 ARC, such the larger case can use the same bullet with slower twist to achieve the same stabilization - a 6 creed spins a 105grn bullet the same angular speed in a 1:8 as a 6 ARC in a 1:7. So if a manufacturer lists a bullet designed with a 6rem, 6 Creed, 243win, etc in mind as requiring a 1:8” twist, they’re bound to get angry phone calls from an unwitting 6 ARC (or 6-45, 6ppc, 6 BR) shooter who has issues stabilizing in a 1:8” barrel, for want of a 1:7” barrel.

It’s really like tying your shoes. None of this is really very complicated, but it does take a little knowledge to understand - once you have it, it’s with you forever.

We are also quite far from the original topic without much definitive results , not that im complaining I've just lost track of where we were.

Maybe it is just tearing my targets at 100 yards. But, I have lower MOA at 300 yards with my 6mmBR Norma and 107 grain Sierras than at 100 yards.

The Yes Men
Lex Webernick of Rifles, Inc. has been building accurate, ultra-lightweight rifles for many years, and as such he tediously tests rifles, barrels and loads at all ranges. He’s an honest Texas craftsmen and many people in the shooting industry know and trust him. Webernick reports that he’s personally seen several rifles consistently shoot equal and even smaller groups at long range than at short range. He said it sometimes takes a few hundred yards for a bullet to ‘go to sleep,’—a term he said was jargon for when a bullet stabilizes into its most accurate, tight spin. Chalk one for the yes column.

Steve Adelmann is a former special forces sniper, a tactical rifle builder/proprietor of Citizen Arms, a respected gun writer and a ballistical nerd. He studies this stuff for a living. He has done extensive testing under controlled conditions for the military.

Adelmann said, “In terms of actual group size, it is possible (especially in light of some of the classified work going on with powered and/or in-flight guided projectiles) but doesn't happen often, and I have only seen it happen at distances very close to each other (i.e. 100 and 200 yards). This is mainly a big bullet issue in either case, and basic physics explain the "why" behind it. I first saw it during early .338 Lapua Mag. testing I did around 2004, especially with 300-grain projectiles. I've seen it in other places from time to time too, especially in heavy subsonic .30 loads and even some supersonic 7.62x39 loads. [That said] I do not think it at all likely that you could get this result consistently with conventional projectiles. I believe it is possible to see from time to time because I have seen it, but only within very narrow parameters—i.e. slow, heavy projectiles that are not fully stabilized out of the barrel but then settle down within a reasonable short distance.”

Adelmann also pointed out that the larger group size could be because when some bullets are fired the nutation (or wobble) is larger and could tear a slightly larger hole on the paper target that is measured, compared to the 200 yard hole that was cut by a bullet that has fully stabilized.

Dave Emary is one of the top ballisticians in the firearm industry. Officially he is Hornady Ammunition’s Chief Ballistic Scientist. He is a contributor to the world standard of guns and ballistics, SAAMI (Sporting Arms and Manufacturers Institute). This organization is comprised of mathematical and technical geniuses and they don’t spout B.S.

Emary said, “It’s not very common, but yes it is possible. It is primarily with very heavy for caliber and long for caliber bullets or bullets that are grossly over-stabilized. In both these cases it can take the bullet a long time to “go to sleep” or to damp out all the “wobble” from the muzzle. This would cause the bullet to shoot better at longer ranges than at short ranges. Several cartridges that exhibit this behavior are the .338 Lapua and the 50 BMG.”

The Conclusion
Based on the opinions I’ve gathered, I think it’s possible that a rifle can be consistently more accurate at long range that at a shorter range, but not likely. If you have a video, or mathematical proof that proves or disproves this phenomenon, please comment below, and let the debate continue.

Well, as has been stated often, Bryan Litz has $10k for the first one of those fellas that steps forward with the data that proves their theory. I believe that offer has been out there for years and no one has even tried to claim it.

I do all my load development at 100 yards and verify my best loads at 500 yards before shooting them in mid range F Class matches. I’ve yet to see an example of precision improving over distance. I’m not claiming to be a ballistics expert, however, if bullets “going to sleep” was simply a function of physics I think I would have seen it in my results.

My observation is this. If my tuned load shoots 5 shot groups into a 1/4 MOA knot at 100, it also shoots 1/4 MOA at 500 yards, sometimes more but never less.

I have a theory as to why some might have the perception that this mystical phenomenon exists. A small statistical sample size of shots fired at close and further distances could account for people believing their 300 yard groups are tighter than their 100 groups. Also, scope parallax error at 100 that is resolved at distance. Lastly, the shooter might tend to focus more at longer distances because it’s harder, therefore, he concentrates more on his mechanics and rifle handling.

Walkalong said:

The wind blows bullets into small groups sometimes, just like it blows them into big ones

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Good point.

A sleepy bullet is a lazy bullet. I want my bullet to be wide awake and fighting to get into that X Ring.

taliv said:

lys, that's an interesting graph. can you link to the source?

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It is from "Primer Output and Initial Projectile Motion for5.56mm and 7.62mm Ammunition" Ritter and Beyer, ARL, Sep 2015.

rkittine said:

"A well behaved bullet will begin it's flight on a center line and move up in the beginning of the arc as it heads down range. As the spin rate declines over distance, at a slower rate then the projectiles decay in velocity, the projectiles gyroscopic stability will increase" Many studies have been done on this, especially with regard to long range shooting.

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Increased stability does not equal decreased dispersion.

The Army has shot thousands (millions?) of rounds through multi-range catch screens* and has yet to report on the dispersion decreasing as range increases.

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* You put a target up at 100 yards, and put up a large blank sheets at 200, 300 400, etc as far out as you want, you just adjust the height of the 100 yard target so as the drop carries it through all the remaining screens. And, now you can compare the dispersion at multiple ranges without having to deal with ammunition variation.

Howa 9700 said:

A couple observations and a question. On observations, have often wondered / marveled......that for a bullet to get moving, not only has to first overcome the inertia of being at rest, but then when it hits the lands, has to also overcome more inertia and start spinning. Have often wondered if bullet has to initially skid a bit, like an airplane tire during landing.

But as for the question........where does twist rate of barrel fit in? If a bullet begins to twist the moment it hits the lands......why does twist rate even matter in this gyroscopic scheme of things?

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If a bullet started to "skid", it means that the shear strength of the outer layer of the projectile, or jacket, has been exceeded. If that is the case, then the rifling will strip the outer layer off the bullet and it will not engage the rifling and will not spin.

Tighter twists just use more of the energy to spin the projectile and there is a minuscule velocity drop. If that worries you use gain twist rifling.

rkittine said:

I think it’s possible that a rifle can be consistently more accurate at long range that at a shorter range, but not likely. If you have a video, or mathematical proof that proves or disproves this phenomenon, please comment below, and let the debate continue.

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That’s the claim made by many, and it sure sounds great, but it remains to be actually demonstrated by anyone in any controlled environment to prove it’s actually happening. Many shooters panic more at short range and will mechanically influence the rifle more, but there’s no scientific backing, nor empirical proof of spiraling bullets which find their centerline. Even with considerable tip yaw, the center of mass of the bullet does not scribe a spiral.

As I said, prove it, instead of just providing anecdotes and name dropping, and plenty of folks - including one long standing publicized purse - are happy to make you a wealthier man.

rkittine said:

The Conclusion
Based on the opinions I’ve gathered, I think it’s possible that a rifle can be consistently more accurate at long range that at a shorter range, but not likely. If you have a video, or mathematical proof that proves or disproves this phenomenon, please comment below, and let the debate continue.

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Based on physics, I am going to say that dispersion must increase with range, and cannot decrease.

We know there are many forces (vectors actually, as they have magnitude and a radial direction) on the bullet that force the bullet away from its initial trajectory path: crossing velocity, pointing angle, CG jump, aerodynamic jump, and muzzle blast.

Crossing velocity - The barrel moves, it starts moving before the bullet leaves the muzzle. Therefore, the velocity of the muzzle and its direction will impart motion to the bullet in a radial direction, aka, away from the stationary line of the bore.
Pointing angle - As we have noted the barrel moves so when the bullet leaves the muzzle the bore is not pointing where it was aimed, there is an angle between the aimed direction and the actual direction it points when the bullet leaves.
CG jump - the force from moving the center rotation from the geometric axis to the axis of the CG.
Aerodynamic jump - The bullet produces lift during its flight, that's how it maintains its stability. Theoretically, if the yaw angle remained constant the lift vector would swing around and cancel out. But, we have seen that the yaw angle does not stay constant, so the lift vector grows and shrinks as it goes around and the net result is a force pushing the bullet off its theoretical path.
Muzzle blast - if the bullet's trailing edge does not break contact with the muzzle perfectly uniformly, high pressure gas will escape in one area before ther rest. This means there will be an area in higher pressure on one side of the bullet, and push it laterally.

All of these vectors act in an outward direction, meaning they push the bullet away from the theoretical trajectory.

Please name the vectors that would act inward, i.e., push the bullet back toward the theoretical trajectory?

To comment on the original topic, I have no experience with bench rest rifles so I am wholly unqualified to comment on that, but in handloading for normal hunting and varmint rifles I have never found bullet jump to be that important unless its an old milsurp rifle or something that has a peculiar chamber cut and you can better support the bullet with a certain amount of jump. Its usually the last part of my reloading process and I usually find its difficult to determine a difference in group size going from say .060" jump to .160" or something like that. There are so many factory rifles that it is impractical to even load a bullet out long enough to reach the rifling that I don't put all that much thought into it anymore.

I have a 25-06 that has the rifling leade so worn out that the bullet jump has increased by like .200" since I started loading for it, but it is entirely unbothered by this.

JDinFbg said:

In some thread somewhere, one guy opined that looking at the vertical spread within a group is another indicator for finding the "sweat spot" load since the vertical spread is less affected by wind. This seems logical, but I can't scientifically verify it.

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Vertical dispersion is an indicator a load is NOT in a node. The barrel is releasing the bullets in varying harmonic positions within the phase.

Fundamentally and inherently, a tightly clustered group will shoot small in no wind, and will shoot small when a skilled wind reader shoots it in big wind. A vertically strung group will NEVER shoot small, as it is inherently vertically strung, and whether there is wind or not, it will be vertically strung. Typically, horizontal OR vertical stringing are easily solved: vertical = not in a node, so increase or decrease powder, while horizontal = seating depth. So personally, I’m NEVER going to camp on a load with vertical stringing and pretend it’s a good load.

JDinFbg said:

In some thread somewhere, one guy opined that looking at the vertical spread within a group is another indicator for finding the "sweat spot" load since the vertical spread is less affected by wind. This seems logical, but I can't scientifically verify it.

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That fella was wrong, ( IMO )several things can cause vertical or horizontal stringing but being in the perverbial "sweet spot" isn't one of them.

There’s a simple matter of geometry that makes vertical shaped groups bad for precision, particularly if your game is to keep all your shots in a scoring circle.

The widest part of the circle is across its diameter. A vertical stringing load combined with a less than perfect wind call stands a better chance of leaking out of the circle.

These pics are from a barrel tuner test I did at 600 yards. The 10 ring is 6”. Both 5 shot groups are sub 1/2 MOA. One is in tune, the other isn’t and the score is reflected in the results.





Those that keep their shots along the water line, or the fat part of the circle, score higher in precision shooting competitions than those that don’t

Yes, and they are close in terms of group size (0.4 MOA vs 0.3 MOA), however, one is bad (not in tune) and the other is good (in tune) and the score shows that