Thread: serious moa question

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

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.