Barrel Length and Twist Rate

[earthquake]

With all of those who shoot the short barrels, i.e.- 22", 20", 18", do you need at least a 1:10 twist rate, so that the bullet gets at least two full rotations in the barrel before exiting, or does that not matter?

I have a loooong barrel I want to cut down to either 22" or 20", but it has a 1:12 twist. I'm worried I won't get enough spin on the bullet if I do that.

I shoot 168 gr. SMK's and am thinking of either sticking with these or trying some 155 Scenars. I don't plan on shooting past 600yds. much.

Thanks.

 

[oneshot onekill]

Re: Barrel Length and Twist Rate

I'm not sure about the whole "2 full rotations" thing. I hadn't heard that until recently. Someone here with more knowledge than me will have to 'splain that one to me.

 

[trilogymac]

Re: Barrel Length and Twist Rate

My last .308 was a 1-11.25 Rock @ 20", #7. Shot great to 800. Sold it to a buddy and I have one in process to replace it that will be 1-11.25 Rock @ 18", #5.5. I have no doubt it will do just fine.

Hope this helps,
Trilogymac

 

[deadly0311]

Re: Barrel Length and Twist Rate

You will be fine, my 19" Rock 1:10 shoots the 155 scenars out to 1K just fine, with the 1:12 you will be fine

 

[CK_32]

Re: Barrel Length and Twist Rate

20" 1:12 Twist
Best to have 1:11.5 Twist for a 20" but its a stock twist rate and it does just fine.

 

[earthquake]

Re: Barrel Length and Twist Rate

Thanks for the tips. What I was thinking (maybe overthinking) was that would you need to get the bullet two full rotations while in the barrel to have enough spin on it to stabilize it when in flight? i.e. - a 1:12 twist rate would need at least a 24" barrel to give a bullet two full rotations (spin) before exiting.

Guess it doesn't really matter. Who has a 20" 1:12 that shoots 168's?

 

[m41]

Re: Barrel Length and Twist Rate

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: COfox</div><div class="ubbcode-body">Thanks for the tips. What I was thinking (maybe overthinking) was that would you need to get the bullet two full rotations while in the barrel to have enough spin on it to stabilize it when in flight? i.e. - a 1:12 twist rate would need at least a 24" barrel to give a bullet two full rotations (spin) before exiting.

Guess it doesn't really matter. Who has a 20" 1:12 that shoots 168's? </div></div>

I have a stock Remington LTR with a 1/12 20" barrel. A outstanding shooter. The LTR actually prefers 175 MK's for some reason but shoots 168's just fine. I also have a Remington PSS cut down to 18",threaded with a Noveske flash suppressor,also 1/12 barrel. It likes the 168 MK's best. The PSS is a tack driver. I have never shot past 500 yards with either.

I can't prove it but I believe the shorter barrels are actually more consistent. My police agency as well as others are now buying 18" bolt guns only.

I think if you get one cut down you will never regret it. No worry's with the two complete bullet spins theory.

 

[FequalsMA]

Re: Barrel Length and Twist Rate

I had a 20 inch 308 with a 1/12 twist. It shot better than I could hold it.
There is no reason a bullet would need to complete two revolutions, or even one for that matter. Just ask Sir Isaac Newton: an object in uniform motion will stay in motion.
A longer barrel will increase your velocity thus increasing your rpm's but the difference is fairly marginal.

Go ahead and cut away

 

[PFCSkoug]

Re: Barrel Length and Twist Rate

bullet stability is all about rpm. as long as your velocities stay high enough to keep the rpms where they need to be you'll be fine.
How many times it spins in the barrel makes no difference

 

[wfjames22]

Re: Barrel Length and Twist Rate

A shorter barrel is stiffer than a longer barrel of similar diameter. Therefore it has less deflection and is potentially more accurate. Here ( http://www.riflebarrels.com/articles/barrel_making/rigidity_benchrest_rifles.htm ) is an article about it.

 

[CK_32]

Re: Barrel Length and Twist Rate

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: COfox</div><div class="ubbcode-body">Thanks for the tips. What I was thinking (maybe overthinking) was that would you need to get the bullet two full rotations while in the barrel to have enough spin on it to stabilize it when in flight? i.e. - a 1:12 twist rate would need at least a 24" barrel to give a bullet two full rotations (spin) before exiting.

Guess it doesn't really matter. Who has a 20" 1:12 that shoots 168's? </div></div>

My 20" is a 1:12.. Your taking the twist of a barrel way to serious.. Just get a stock barrel and shoot it.. You'll be fine.. they have found twist rates that work already.. Just stick with those.

 

[carbinero]

Re: Barrel Length and Twist Rate

Needing two full turns to stabilize is completely arbitrary and a fallacy: laws of physics do not care about that. Consider the length of a pistol barrel. This issue should be of absolutely no concern when deciding barrel length.

 

[earthquake]

Re: Barrel Length and Twist Rate

Great info guys...thanks again!