MOA at one distance,but not others.

[1SevenZero]

I hear people talk about their rifles shooting MOA, or sub up to certain distances, but then shooting worse than MOA after exceeding that distance. Is that possible?

To me it seems if a rifle is mechanically MOA capable at one distance than it would be capable at all distances.

I would think this would be the result of shooter error, or poor performing loads.

 

[Joe King]

Yes it is very possible. But your right it's usually the nut yankin on the trigger thats to blame, then the loads aren't up to snuff for one reason or another

 

[D.ID]

I have a rifle that groups 1moa at 400 and 1.5 moa at 100. Impossible you say? Certainly seems insane and mechanically impossible to me. But.....it does ....I can't explain it but I can prove it. It does it every time. Some rounds are just limited in optimum performance, for instance I have an evil semi auto in 7.62x39 which will hold 1.5 moa at 100, 2 moa at 200 and good luck pal at 300. It's "optimal" performance range is a couple hundred yards and after it leaves that area of speed vs weight vs aerodynamics it falls on it's face. Everything has an optimal performance range. Your big bad muscle car is weak at 800rpm, mean at 5500rpm and counter productive (all over the hi-way in pieces) at 1100rpm.

 

[1SevenZero]

I hear what you guys are saying, but I'm just not convinced. Can anyone explain the science behind why it would happen?

I've been doing more research and found an interesting thought someone else had. They felt it was more of an optics issue dealing with PARALLAX. I think they could be onto something.

Here is a link to the blog. It's a response near the middle of the comments.

Ask Foghorn: Do groups "tighten up" at longer distances? | The Truth About GunsThe Truth About Guns

 

[D.ID]

I have a rifle that groups 1moa at 400 and 1.5 moa at 100. Impossible you say? Certainly seems insane and mechanically impossible to me. But.....it does ....I can't explain it but I can prove it. It does it every time. Some rounds are just limited in optimum performance, for instance I have an evil semi auto in 7.62x39 which will hold 1.5 moa at 100, 2 moa at 200 and good luck pal at 300. It's "optimal" performance range is a couple hundred yards and after it leaves that area of speed vs weight vs aerodynamics it falls on it's face. Everything has an optimal performance range. Your big bad muscle car is weak at 800rpm, mean at 5500rpm and counter productive (all over the hi-way in pieces) at 1100rpm.

11000rpm not 1100.........................

 

[Joe King]

I hear what you guys are saying, but I'm just not convinced. Can anyone explain the science behind why it would happen?

I've been doing more research and found an interesting thought someone else had. They felt it was more of an optics issue dealing with PARALLAX. I think they could be onto something.

Here is a link to the blog. It's a response near the middle of the comments.

Ask Foghorn: Do groups "tighten up" at longer distances? | The Truth About GunsThe Truth About Guns

Brian Litz has seen the same thing, and with all the knowledge, experience and resources available to him and those that lended a hand in his book's they had no solid answer for that one but a pretty strong theory. I'm sure parallax could be to blame in some instances, it doesn't explain that phenomenon all the time. The Epicyclic theory and a combination of both explains the rest.

Epicyclic Swerve

 

[RTK]

I asked this question before and I believe the answer below by long time range is the most logical and best answer rooted in fact.....

I closely monitored a military test years back at white sands missile range studying the effects of bullet stabilization at extended ranges. When you shoot a group your rifle is not throwing one shot this way and another that unless you are a bad shot. Slow motion photography revealed the bullet is actually traveling in an eliptical path around the centerline of the bore as it travels downrange. As the range increases the elliptical orbit decreases in proportion to the range. Therefore a rifle may shoot a 1" group at 100 yards and a 2.5" group at 500 yards. In other words the bullet is printing on the target dependent on it's position within that eliptical orbit. Some call it going to sleep among other things. The bullet is not continuing it's travel outward from the centerline of the bore at that rate as it travels downrange. At the 200 yard target that same bullet that hit high at 100 could hit low in the group or the one right could hit left depending on where it is within that elliptical orbit. That is about as simple as I can explain a bullet going to sleep as it travels downrange. It is actually stabilizing around the centerline of the bore. With some rifles that can be dramatic in the first couple hundred yards then stable out to be a great shooter at long range. With better quality control barrels now days a good rifle is typically more stable at close range than in the past allowing for a better rifle to rifle average of super tight 100 yard groups. But an over the counter barrel that is not a tack driver at 100 yards can still shoot well at long range. I rarely shoot under 300-400 yards and go out from there so I take most of this effect out and just want to know at the distance I most encounter game how predictable the rifle is.
__________________

 

[Bart B]

In Sierra Bullets' tests, they've learned that virtually all rifle bullets have spin stabilized by 100 yards.

If one stops and thinks about simple exterior ballistics, they'll easily learn why a 1/2 MOA system won't be a 1/2 MOA system at 1000 yards. Two main ballistic reasons.....

One's muzzle velocity spread. .308 Winchesters with a 50 fps muzzle velocity spread will have about 1/10th inch vertical shot stringing at 100 yards. Check this with any online ballistics software. Then go back to the 1000 yard line and you'll see that vertical shot stringing is about 20 inches.

The other's ballistic coefficient; it ain't the same for all bullets of a given make, model and caliber. As they ain't all perfectly balanced, they wobble a bit in flight; the more wobble the more drag they have. Sierra Bullets sees about a 1 to 2 percent spread across a batch of match bullets due to bullet imbalance. Use ballistic software to see what that spread in BC will cause in bullet drop for a given bullet at a given muzzle veloctiy.

And one environmental reason.... possibly two.....

The air on this planet's not perfectly still. Subtle wind movements exist even when flags show no movement whatsoever. These stubtle winds cause horizontal shot stringing. The longer a bullet's in the air, the more those subtle cross winds will move it. To say nothing of the slight differences in air density bullets go through enroute to the target; they ain't all the same, either.

I've done some checking on test groups fired at short and long ranges and came up with the following. Groups at 100 yards typcally get about 15% larger for each 100 yards further down range. .5 moa at 100, .575 moa at 200, .661 at 300, .760 at 400, .875 moa at 500 and so on.

One exception's when a barreled action has a lot of whip such that bullets leaving slower do so at a greater muzzle axis angle than the faster ones leaving at lower angles. The Brit's SMLE .303's are famous for this and with arsenal ammo with big muzzle velocity spreads, they shot very accurate from 700 yards and beyond. At the shorter ranges, they didn't do as well as Mauser 98 action rifles do. No wonder their SMLE's won so many long range matches.

'Tis another myth that groups keep their same angular dispersion from close at hand to all the way to some distant point. After all, don't all bullets shoot 0 moa at the muzzle?

 

[Broz]

After all, don't all bullets shoot 0 moa at the muzzle?

I loaded some that didn't....

J/K Bart...

Jeff

 

[Boss Hoss]

In Sierra Bullets' tests, they've learned that virtually all rifle bullets have spin stabilized by 100 yards.

If one stops and thinks about simple exterior ballistics, they'll easily learn why a 1/2 MOA system won't be a 1/2 MOA system at 1000 yards. Two main ballistic reasons.....

One's muzzle velocity spread. .308 Winchesters with a 50 fps muzzle velocity spread will have about 1/10th inch vertical shot stringing at 100 yards. Check this with any online ballistics software. Then go back to the 1000 yard line and you'll see that vertical shot stringing is about 20 inches.

The other's ballistic coefficient; it ain't the same for all bullets of a given make, model and caliber. As they ain't all perfectly balanced, they wobble a bit in flight; the more wobble the more drag they have. Sierra Bullets sees about a 1 to 2 percent spread across a batch of match bullets due to bullet imbalance. Use ballistic software to see what that spread in BC will cause in bullet drop for a given bullet at a given muzzle veloctiy.

And one environmental reason.... possibly two.....

The air on this planet's not perfectly still. Subtle wind movements exist even when flags show no movement whatsoever. These stubtle winds cause horizontal shot stringing. The longer a bullet's in the air, the more those subtle cross winds will move it. To say nothing of the slight differences in air density bullets go through enroute to the target; they ain't all the same, either.

I've done some checking on test groups fired at short and long ranges and came up with the following. Groups at 100 yards typcally get about 15% larger for each 100 yards further down range. .5 moa at 100, .575 moa at 200, .661 at 300, .760 at 400, .875 moa at 500 and so on.

One exception's when a barreled action has a lot of whip such that bullets leaving slower do so at a greater muzzle axis angle than the faster ones leaving at lower angles. The Brit's SMLE .303's are famous for this and with arsenal ammo with big muzzle velocity spreads, they shot very accurate from 700 yards and beyond. At the shorter ranges, they didn't do as well as Mauser 98 action rifles do. No wonder their SMLE's won so many long range matches.

'Tis another myth that groups keep their same angular dispersion from close at hand to all the way to some distant point. After all, don't all bullets shoot 0 moa at the muzzle?

Bart--might contact Big Green again. The 100 yd information is more like 300. Maybe your information is a little older but I was discussing this earlier this year with my shooting partner that works there. Maybe Kevin Thomas is watching this and can weigh in.

 

[Bart B]

Bart--might contact Big Green again. The 100 yd information is more like 300. Maybe your information is a little older but I was discussing this earlier this year with my shooting partner that works there. Maybe Kevin Thomas is watching this and can weigh in.

I agree, Kevin's input would be (and always is) worthwhile.

From Big Green's web site 3 minutes ago:

Coning motions are caused by side forces applied to each bullet as it exits the muzzle, but in all but very severe cases the coning motion will damp out within about 100 yards downrange from the muzzle.

That's probably from an earlier loading manual from Sierra. And maybe things have changed since then.

'Tis interesting that benchrest record groups and aggregates get bigger in MOA as one looks at their numbers at 100, then 200 and finally 300 yards.

 

[Joe King]

If one stops and thinks about simple exterior ballistics, they'll easily learn why a 1/2 MOA system won't be a 1/2 MOA system at 1000 yards. Two main ballistic reasons.....

Maybe maybe not, it happens that some rifles do produce better accuracy at more distant ranges than closer, it's been proven out by those much better qualified and equipped by you and I.

One's muzzle velocity spread. .308 Winchesters with a 50 fps muzzle velocity spread will have about 1/10th inch vertical shot stringing at 100 yards. Check this with any online ballistics software. Then go back to the 1000 yard line and you'll see that vertical shot stringing is about 20 inches.

The other's ballistic coefficient; it ain't the same for all bullets of a given make, model and caliber. As they ain't all perfectly balanced, they wobble a bit in flight; the more wobble the more drag they have. Sierra Bullets sees about a 1 to 2 percent spread across a batch of match bullets due to bullet imbalance. Use ballistic software to see what that spread in BC will cause in bullet drop for a given bullet at a given muzzle veloctiy.

The effect is so small that the only way it can be measured is by a mathematical equation.

And one environmental reason.... possibly two.....

The air on this planet's not perfectly still. Subtle wind movements exist even when flags show no movement whatsoever. These stubtle winds cause horizontal shot stringing. The longer a bullet's in the air, the more those subtle cross winds will move it. To say nothing of the slight differences in air density bullets go through enroute to the target; they ain't all the same, either.

How does this ^ explain this-->

I have a rifle that groups 1moa at 400 and 1.5 moa at 100. Impossible you say? Certainly seems insane and mechanically impossible to me. But.....it does ....I can't explain it but I can prove it. It does it every time.

I've done some checking on test groups fired at short and long ranges and came up with the following. Groups at 100 yards typcally get about 15% larger for each 100 yards further down range. .5 moa at 100, .575 moa at 200, .661 at 300, .760 at 400, .875 moa at 500 and so on.

you shooting in a massive warehouse?

One exception's when a barreled action has a lot of whip such that bullets leaving slower do so at a greater muzzle axis angle than the faster ones leaving at lower angles. The Brit's SMLE .303's are famous for this and with arsenal ammo with big muzzle velocity spreads, they shot very accurate from 700 yards and beyond. At the shorter ranges, they didn't do as well as Mauser 98 action rifles do. No wonder their SMLE's won so many long range matches.

+

If one stops and thinks about simple exterior ballistics, they'll easily learn why a 1/2 MOA system won't be a 1/2 MOA system at 1000 yards. Two main ballistic reasons.....

=
What!?!?

'Tis another myth that groups keep their same angular dispersion from close at hand to all the way to some distant point. After all, don't all bullets shoot 0 moa at the muzzle?

I wish load development would a snap if they did

 

[Bart B]

About my comments regarding a 1/2 MOA system at 100 won't be a 1/2 MOA system at 1000 yards. . . .

Maybe maybe not, it happens that some rifles do produce better accuracy at more distant ranges than closer, it's been proven out by those much better qualified and equipped by you and I.

So, what qualifications and equipment must I have to prove anything about that?

Please let me know what you think my qualifications are and what equipment I've got and I'll see if they match what reality is.

And note I've already mentioned one exception stating one rifle known world wide in long range competition that shoots better at the longer ranges than the shorter ones. I didn't mention the M14 US service rifle that does the same thing as the SMLE's but to a lesser degree. Therefore, I already know that "some" rifles do shoot better at longer ranges compared to shorter ones.

 

[rscott5028]

Brian Litz has seen the same thing, and with all the knowledge, experience and resources available to him and those that lended a hand in his book's they had no solid answer for that one but a pretty strong theory. I'm sure parallax could be to blame in some instances, it doesn't explain that phenomenon all the time. The Epicyclic theory and a combination of both explains the rest.

Epicyclic Swerve

That's a great article. But, you failed to read or understand his conclusion.

Bryan pretty much tried everything he could to mathematically force Epicyclic Swerve to explain the phenomenon. In the end, he stated that it just isn't a big enough factor to explain even as much as a caliber's worth of swerve.

Paralax, marksmanship, and statistical sampling error are the most common causes.

-- richard