Thread: serious moa question

If its anything It will just be the parallax being set at longer range / being out of parra up close.

Pitching and Yawing of a bullet - YouTube

Originally Posted by Tui4Me

Pitching and Yawing of a bullet - YouTube

Thanks for posting that is interesting

There are others out there with much more scientific knowledge then I have on the subject. What I have is practical real world experience and this is what I have learned from shooting very long bullets to high velocity in fast twist barrels. Here are a few things I have learned:

The bullet is not unstable when it leaves the barrel, BUT, what is happening is that as the bullet is in the barrel, it is forced to rotate around the axis of the bore. When the bullet exits the bore, the bullet then will try to spin around its center of gravit. This is seldom exactly the same point as the axial center of the bore. AS such, there is some "wobble" if you will in the bullet.

This happens until the bullet settles down or "goes to sleep" and spins true around its center of gravity. Think of it like a childs toy top. When you first release it it will have some wobble and it will also move around a bit on the ground, then it stabilizes and spins much more even and true. Same thing happens with the bullet.

here are some general things I have found to be true:

1. The longer the bullet, the more range it takes for the bullet to fight off the effects of the rifling and spin true around its own center of gravity.

2. The faster the twist, often the more you will see this.

3. The higher the velocity, often the more you will see this.

If you take a conventional bullet, it also does this but the relatively low weight of the bullet and its relatively short length do not show this as far down range

For example, a 50 BMG will often take 250 to 300 yards for the bullet to completely go to sleep and spin true. My 7mm AM for instance will be very similiar to this shooting a 200 gr ULD RBBT as will the 338s based on the 408 CT case.

In most cases, with conventional chamberings, this range is more like 100 to 150 yards. In most varmint chamberings with low bullet weight, its generally well under 100 fps.

So how do you know?????

Well, the best way is simply to measure groups at various ranges. If the rifle is accurate and the load is a good consistant load, its relatively easy to do. For example, many of my personal heavy rifles will shoot 1/2 moa at 100 yards. At 300 yards, the group size will often be 1/3 moa. At 500 yards, its not uncommon to see 1/4 moa. That this tells me is that once you get past 300 yards or so, the bullets are generally shooting nearly the same or smaller moa group levels out to very long range.

It is not uncommon at all to see this type of rifle shooting very long, very heavy bullets at high velocity out of a fast twist barrel to see a load that shoots 3/4 moa at 100 yards that can shoot 1/2 moa or even less at 500 yards.

Most believe that once a bullet is sent on its path in flight, the groups it forms will be conal in shape. That is generally not the case with a heavy, long bullet.

Now this is really a simplistic way to look at it but it happens time and again. It has nothing to do with stability really, its just the bullet trying to fight off the forces impossed by the rifling and fly true and spin around its own center of gravity.

Again, I am sure many will read this and say the terminology is wrong and I am sure it is but I believe the ideas are sound from what I have seen testing many rifles with this type of bullet.

With conventional weight and velocity bullets, it will be much harder to see if possible at all.

Kirby Allen(50)
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Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: Home Page

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The parallax setting of your scope could be a factor ,I believe most most US made hunting scopes are factory set for 100 150 yards .

The thing that surprises me is the number of hunting rifles that now consistently shoot MOA or less groups at all sort of distances ,In my experience and from what I have seen these MOA's are seldom shot in competition or in practice sessions at public /NZDA ranges , so the MOA must be a shy little thing that only comes out in private . Finding the windless conditions for shooting the elusive MOA at longer ranges in NZ , can be extremely difficult.
Shooting a MOA group is one thing , being able to place 5 shots within 1 MOA of the point of aim ( center of the bull) is another thing entirely , one is to do with equipment , the other to do with ability .

Originally Posted by Tui4Me

There are others out there with much more scientific knowledge then I have on the subject. What I have is practical real world experience and this is what I have learned from shooting very long bullets to high velocity in fast twist barrels. Here are a few things I have learned:

The bullet is not unstable when it leaves the barrel, BUT, what is happening is that as the bullet is in the barrel, it is forced to rotate around the axis of the bore. When the bullet exits the bore, the bullet then will try to spin around its center of gravit. This is seldom exactly the same point as the axial center of the bore. AS such, there is some "wobble" if you will in the bullet.

This happens until the bullet settles down or "goes to sleep" and spins true around its center of gravity. Think of it like a childs toy top. When you first release it it will have some wobble and it will also move around a bit on the ground, then it stabilizes and spins much more even and true. Same thing happens with the bullet.

here are some general things I have found to be true:

1. The longer the bullet, the more range it takes for the bullet to fight off the effects of the rifling and spin true around its own center of gravity.

2. The faster the twist, often the more you will see this.

3. The higher the velocity, often the more you will see this.

If you take a conventional bullet, it also does this but the relatively low weight of the bullet and its relatively short length do not show this as far down range

For example, a 50 BMG will often take 250 to 300 yards for the bullet to completely go to sleep and spin true. My 7mm AM for instance will be very similiar to this shooting a 200 gr ULD RBBT as will the 338s based on the 408 CT case.

In most cases, with conventional chamberings, this range is more like 100 to 150 yards. In most varmint chamberings with low bullet weight, its generally well under 100 fps.

So how do you know?????

Well, the best way is simply to measure groups at various ranges. If the rifle is accurate and the load is a good consistant load, its relatively easy to do. For example, many of my personal heavy rifles will shoot 1/2 moa at 100 yards. At 300 yards, the group size will often be 1/3 moa. At 500 yards, its not uncommon to see 1/4 moa. That this tells me is that once you get past 300 yards or so, the bullets are generally shooting nearly the same or smaller moa group levels out to very long range.

It is not uncommon at all to see this type of rifle shooting very long, very heavy bullets at high velocity out of a fast twist barrel to see a load that shoots 3/4 moa at 100 yards that can shoot 1/2 moa or even less at 500 yards.

Most believe that once a bullet is sent on its path in flight, the groups it forms will be conal in shape. That is generally not the case with a heavy, long bullet.

Now this is really a simplistic way to look at it but it happens time and again. It has nothing to do with stability really, its just the bullet trying to fight off the forces impossed by the rifling and fly true and spin around its own center of gravity.

Again, I am sure many will read this and say the terminology is wrong and I am sure it is but I believe the ideas are sound from what I have seen testing many rifles with this type of bullet.

With conventional weight and velocity bullets, it will be much harder to see if possible at all.

Kirby Allen(50)
__________________
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: Home Page

allenmagnum@gmail.com

He's talking about epicyclic swerve which is explained by Bryan Litz in the article I linked earlier. It exists but is of very small magnitude and is not the cause of this effect.

If such is the case, then bullet BC will INCREASE at distance as so called stability increases
The centrifugal forces on the bullet are still there in the barrel, they don't magically start when it exits the barrel, infact they are reducing from the moment it leaves the muzzle
A long bullets centrifugal force is no different to a short one at the same rpm
The CoG is still in the centre and the diameter hasn't changed

Originally Posted by Druid

The parallax setting of your scope could be a factor ,I believe most most US made hunting scopes are factory set for 100 150 yards .

The thing that surprises me is the number of hunting rifles that now consistently shoot MOA or less groups at all sort of distances ,In my experience and from what I have seen these MOA's are seldom shot in competition or in practice sessions at public /NZDA ranges , so the MOA must be a shy little thing that only comes out in private . Finding the windless conditions for shooting the elusive MOA at longer ranges in NZ , can be extremely difficult.
Shooting a MOA group is one thing , being able to place 5 shots within 1 MOA of the point of aim ( center of the bull) is another thing entirely , one is to do with equipment , the other to do with ability .

The above is very true and I'd put myself in this category too. I can at times do some reasonable shooting, but throw in wind and other variables and that shooting deteriates remarkably. But on those windless days or on an Nzda range with wind flags I can usually figure it out and not totally make a fool of myself ...but I certainly can't claim to hold the same POI all day every day at all ranges, as that's not true. And that me (the shooter) and not so much my gear.

Kj

Ive read this as well, it sounds silly, yet its been commented on enough with different ppl that I'd like to get a real/proper/true explanation.

Shooting through paper sounds an excellent way to test....if we see a decreased dispersion thats going to be one hell of a wtf moment.....not that I think we will.

Originally Posted by gimp

And if you stop and think about it, how can it possibly do that from a physical standpoint?? How can the rate of angular dispersion decrease? It's like shooting a 5 shot group by throwing 5 curveballs that all curve out in different directions then back in again to the same point. There's nothing to make a bullet "going to sleep" actually point back inwards in relation to flight after flying off erratically due to poor stability.

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.”

As much as I appreciate your 'professional' testimonials Gimp, ill side with the general consensus of the experts on this one...I'd stick to spell checking and sarcastic comments.

Why not start with this reply?

I'm presuming you copy+pasted that from here where there are a bunch of people saying they've never seen it and it can't happen as well as the opposite. There's no consensus amongst ~*the professional experts*~

American Hunter - Can a Rifle's Accuracy be More Consistent at Long Range than it is at Short Range?



It's counter to logic and while "going to sleep" is a thing, I don't see how it can cause this effect. Someone go shoot through a piece of paper at 100 and at a target at 300 with the same shots and see what happens. It's the only way to really come to any conclusion.

I plan to try shooting at a target at 500yards whilst punching through some sort of light clear plastic sheets along the way.

Not sure what to shoot through as we dont want to disturb the path of the bullet at all?

some sort of very thin paper would be ideal. I will try it as soon as I can.

To test this I believe you would need to do it in perfect shooting conditions with a rifle capable of shooting at least 1/2 MOA at 500 yards.

There will be no point aiming at and punching through paper at 100 yards in windy conditions as your test target 400yards further downrange will be effected by wind drift.

I think you really need to wait to good shooting conditions where you know you will get small tidy groups, set a target you will be aiming at 500yards and have sheets of clear stretch wrap or something set up 100yards ahead of the shooter?

Also getting the paper centered over that distance would be an issue wouldn't it?