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Posted: 12/26/2012 8:08:35 AM EDT
Looking to stabilize 77gr Hornady BTHP projectiles for 500 yard range accuracy.

Can this be achieved with 1:7 barrel less than 16" or am I asking for too much from a shorter barrel?

Thx!
Link Posted: 12/26/2012 8:36:54 AM EDT
With 5.56 level Mk262 ammo? ~12.5".
Link Posted: 12/26/2012 9:47:47 AM EDT
Originally Posted By RedFalconBill:
With 5.56 level Mk262 ammo? ~12.5".


Where does that number come from? I'm sure a lot of people with 10.5" and 11.5" barrels would like to know. I've never gotten a keyhole from my 10.5" barrel.
Link Posted: 12/26/2012 12:54:09 PM EDT
Barrel length has no direct relationship to bullet stabilization but muzzle velocity does. Basically the longer the barrel the greater the muzzle velocity and the higher the rotational speed of the bullet when it exits the bore.
Link Posted: 12/26/2012 4:24:37 PM EDT

Originally Posted By GeneralPurpose:
Originally Posted By RedFalconBill:
With 5.56 level Mk262 ammo? ~12.5".

Where does that number come from? I'm sure a lot of people with 10.5" and 11.5" barrels would like to know. I've never gotten a keyhole from my 10.5" barrel.

Comes from what MV is needed to ensure that the projectile is still supersonic in all field conditions.

It also looks like I was wrong and that you could shoot Mk262 out of a barrel as short as 9", or so, and still be supersonic at 500yds with some comfort.

Sorry, if I caused any feathers to be ruffled.
Link Posted: 12/26/2012 4:32:09 PM EDT

Originally Posted By GeneralPurpose:
Originally Posted By RedFalconBill:
With 5.56 level Mk262 ammo? ~12.5".


Where does that number come from? I'm sure a lot of people with 10.5" and 11.5" barrels would like to know. I've never gotten a keyhole from my 10.5" barrel.


My 11.5 doesn't agree with this comment.

Link Posted: 12/26/2012 5:05:09 PM EDT
Based on my ballistic calculator and the velocity data from this post Velocity/Barrel Lenght a 7.5 inch barrel with 77gr MK262 would cross into subsonic velocities at nearly exactly 500 yards. So you could possible do this but I think this would be the absolute limit. The bullet drop would be significant at 125 inches at 500 yards. More like shooting artillery.

But if I wanted the perfect combination of portability of my rifle and yet effective velocity out to 500 yards using MK262, I would definitely go with a 12.5 inch barrel. Bullet drop here is 86 inches and it is still supersonic up to 675 yards.

This is my opinion and what I would do. Thanks.
Link Posted: 12/26/2012 10:28:59 PM EDT
Originally Posted By RedFalconBill:

Originally Posted By GeneralPurpose:
Originally Posted By RedFalconBill:
With 5.56 level Mk262 ammo? ~12.5".

Where does that number come from? I'm sure a lot of people with 10.5" and 11.5" barrels would like to know. I've never gotten a keyhole from my 10.5" barrel.

Comes from what MV is needed to ensure that the projectile is still supersonic in all field conditions.

It also looks like I was wrong and that you could shoot Mk262 out of a barrel as short as 9", or so, and still be supersonic at 500yds with some comfort.

Sorry, if I caused any feathers to be ruffled.


I see, I was looking at bullet stabilization as the bullet being stable when it leaves the barrel, not the distance at which it enters the trans-sonic region and becomes unstable downrange.
Link Posted: 12/26/2012 10:51:33 PM EDT
Originally Posted By Russ4777:
Barrel length has no direct relationship to bullet stabilization but muzzle velocity does. Basically the longer the barrel the greater the muzzle velocity and the higher the rotational speed of the bullet when it exits the bore.


This...
Link Posted: 12/27/2012 4:50:35 PM EDT
according to the Berger bullet stabilzation calculator, that bullet would be adequately stable at 1050fps....you'd be getting way more fps than that from a full power load in any usable barrel length.

advntrjnky
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