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Posted: 2/22/2006 4:50:05 AM EDT
First off, I have read thru the Ammo Oracle and I didn’t see the answer to my question. If the answer to my question is in there please show me where.

I am looking at a M4 type barrel. I want to go with a 14.5 with a perm phantom flash hider, chrome lined. I would like to go with a 1/9 if possible. My question is will a 14.5” 1/9 barrel stabilize a Black Hills 68 gr OTM? When I read thru the ammo oracle I saw that a 1/9 will stabilize it, but I didn’t see where it talked about barrel length.

Has anyone done any real world testing with a 14.5” barrel and 68 gr ammo. I have a 16” chrome lined 1/9 that seems to work well with BH 68 gr at 100 yds. I just want to make sure that taking 1.5” off the barrel will not affect the ability of the barrel to stabilize the bullet.
Link Posted: 2/22/2006 5:19:14 AM EDT
The length of the barrel (unless it is ridiculously short like a 1/2") should have no bearing on whether or not the bullet is stabilized.

The 68gr shoot fine out of my 1:9's
Link Posted: 2/22/2006 5:24:21 AM EDT
[Last Edit: 2/22/2006 5:27:43 AM EDT by eagle308us]

Originally Posted By stratsandaks:
The length of the barrel (unless it is ridiculously short like a 1/2") should have no bearing on whether or not the bullet is stabilized.

The 68gr shoot fine out of my 1:9's



Why is that. I would assume that the shorter the barrel the less time that the bullet is in the barrel. Less time in the barrel would equal less spin on the bullet which could affect the stability?

In a 14.5" 1/7 you will get 2 full turns on a bullet. In a 14.5" 1/9 you will get about 1.75 turns. Is this logic correct?

I am by no means an engineer.
Link Posted: 2/22/2006 7:01:07 AM EDT

Originally Posted By eagle308us:

Why is that. I would assume that the shorter the barrel the less time that the bullet is in the barrel. Less time in the barrel would equal less spin on the bullet which could affect the stability?

In a 14.5" 1/7 you will get 2 full turns on a bullet. In a 14.5" 1/9 you will get about 1.75 turns. Is this logic correct?

I am by no means an engineer.



The barrel length will have no affect on stabilization unless the length is something ridiculously short for an AR 15, like 1 or 2 inches (which I don't think is even possible using a gas system). The bullet enters immediate twist after leaving the throat and is pretty much spinning at the same rate then as it will when it leaves the barrel. Barrel length will affect MV, however, which can affect your practical range, but stability should be no problem.

Accuracy can also suffer with shorter barrels, but not because of stability from a lack of rotation. Longer barrels not only give the bullet more time to "settle down" and fly straighter, but also lengthen your sight radius.

Hope this helps. I had the same misunderstandings when I was looking into buying my AR15.
Link Posted: 2/22/2006 10:34:58 AM EDT
You will have no problems with the 68gr in a 1/9 barrel of any length. A 75gr on the other hand is hit or miss with 1/9's.
Link Posted: 2/22/2006 10:53:31 AM EDT
The 68 will work fine in a 1-9 like the one you're describing.


As for barrel length - it DOES matter. Not because the barrel is longer, but because a longer barrel creates greater velocity. Greater velocity through the same twist generates more RPM's on the bullet. That means greater stabilization.


For example,


A 16" barrel let's say gives you 2700fps for the 68. A 24" barrel gives you 3000fps. Both are 1/9 twists. The length has nothing to do with the stabilization, but the increased velocity that the 24" barrel produces does.


A bullet traveling through a 1/9 twist @ 3000 fps will have more RPM's than the very same bullet going through that 1/9 twist @ 2700 fps.
Link Posted: 2/22/2006 11:12:41 AM EDT
SIMPLE yes good to go!

I have 1/9 Bushmaster 15HBAR that shoots the 69 bthp very tight!

Before some DUMB ASS quotes me !!!!

its was a 16 incher until kurt did some work on it!
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