Barrel length & Bullet Stability

[starislon]

Can anyone tell me me to what degree, if any, a longer barrel affects bullet stability over a shorter barrel. Say one is 16" and the other is 28", and both with the same rate of twist, & both, of course, firing the same bullet in the same caliber.

If a longer barrel does help stabilize the bullet, could a bullet that was unstable in, say a 16" barrel, become stable in a 30" barrel, both barrels having the same twist? Just curious.

Read More

 

[whphel]

I know that out of a longer barrel the bullet will be moving faster than the shorter barel I belive you gain 27fps per 1". I will check with my friends at Benchmark Barrels and get back to you but this is all physics and the info can be obtaind on line.

 

[Gunner3456]

Don't forget the issue of powder. A powder which burns just fast enough for that 16" might be all burned up before the bullet reaches the end of that (very much) longer barrel. That's assuming you're using the same cartridges...

 

[starislon]

Thanks for your responses.

My main concern Re bullet 'stability' is how it affects long range accuracy, rather than fps, although I think fps can also have an affect.

I guess it boils down to this: If, for example, a .223 rifle with a 1:12 twist rate and a 16" barrel shoots 77 grain cartridges to poor effect, will the accuracy improve if the same 77 grain bullet is shot out of a 1:12 twist barrel that is 28" long? And if so by a lot or a little?

I have a 28" 1:12 twist barrel coming my way, but if a 77 grain bullet will never stabilize in it, I'll stay away from them and limit my shooting to the bullets it will shoot accurately.

thanks again for your responses.

 

[whphel]

From what i know you would need a longer barrel with that twist rate to stablize a 77gr .223 bullet but if the twist rate was 1:7 you can reduce the charge out of a shorter barrel and it will be stable and carry farther alltho be it with less speed and energy. But like I said earlyer I will pass this info along to thoughs who know much more than I. I am sill learning and in this hobby/sport there is much to learn.

 

[starislon]

whpel:


Thanks for your response. I think you got it right, if I want to shoot 77 grain bullets accurately I'm going to have to get a 1:7 or 1:8 twist barrel.

 

[whphel]

Or a longer 1:10 or 1:12. Like I said before I'm not a gun smith and don't build barrels but I know guys that do and there very good barrels.

 

[Green Rabbit]

The idea is that bullet needs to get certain rotation speed in order to be stable.
This is easier to achieve for lighter (and thus faster) bullets, since it passes through rifling faster and thus rotates at greater RPMs. Longer barrel may help as long as muzzle velocity increases, but heavy bullets it may never reach needed speed even in 28" barrels

In the other hands, high twist rate adds more friction and slows down the bullet

Here you can find some recommendations about twist rates for different weight bullets:

http://www.6mmbr.com/223Rem.html

 

[whphel]

Here is a good article and usfull info for your research.

http://www.snipercountry.com/hottips/TwistRate.htm

Here is a Barrel twist rate calculator that you may want to play with.
http://kwk.us/twist.html

 

[torpedoman]

in a 22 the powder is gone and the bullet is moving as fast as it will get at 16 in however it will be more accurate at 20 in even if it is moving a bit slower. center fires work the same depending on the powder you are using. if the powder is all burnt that bullet is moving as fast as it will get (pressure being max) futher travel in the barrel will decrease speed due to friction and pressure droppinghowever accuracy may (or may not) increase. if using iron sights you get a longer sight radius which always increases accuracy.

 

[XOR]

Can anyone tell me me to what degree, if any, a longer barrel affects bullet stability over a shorter barrel. Say one is 16" and the other is 28", and both with the same rate of twist, & both, of course, firing the same bullet in the same caliber.

If a longer barrel does help stabilize the bullet, could a bullet that was unstable in, say a 16" barrel, become stable in a 30" barrel, both barrels having the same twist? Just curious.

I've seen lightweight bullets in 16" M1A keyhole at 25M but the same exact bullet was punching perfect holes from the standard length 22" M1A barrel. It definitely affected accuracy.

Further, the longer barrel will give you a better sight radius for iron sights which means it will be much less sensitive to shooter errors at distance.

 

[Green Rabbit]

in a 22 the powder is gone and the bullet is moving as fast as it will get at 16 in

This is not true. Even if the powder is gone - the pressure is still there. And the bullet accelerates by the pressure, not by the burning powder. It won't be accelerating as fast as on the max pressure, but still will be accelerating.
And the speed begin to decrease only when force of the friction will exceeds the force created by the hot gas pressure. Which is, in any practical barrel length, not going to happen