1:7 vs. 1:9 on 10.5" barrel

[idleclamp]

Hi everyone,

While I'm waiting for a Form 1 to get back to me, I've been doing research what twist to get in a barrel. I've received good arguments for both, and that's the only twist I can find for a 10.5" barrel.

My SBR will have a suppressor on it, so baffle strikes are a concern, especially if I want to try and slow it to subsonic, which is the argument for the 1:7 to get heavy bullets spinning in 10.5 inches. So is a 1:7 twist necessary to get a heavy bullet spinning (69-95 grains)?

The next argument I was told is that if I want to shoot 55 grainers, a 1:7 will spin the jacket off of the bullet, hence needing a 1:9. I don't know enough about it to make a good educated decision and have heard arguments both ways which is why I'm posting.

 

[superA]

1 in 7 will not spin the jackets off of the 55 grainers. Basically it just comes down to what you will shoot the most. If you want to shoot heavy stuff out of it though 1 in 7 will be the way to go especially in a short barrel.

 

[Spiff]

For almost all intents and purposes, there is no disadvantage to using a 1:7 twist for 5.56/.223. 1:9s have been known to not stabilize 75s. In a short barrel you want all the twist you can get, because you're going to have lower RPMs due to the lower muzzle velocity.

If 1:7s spun the jackets off of 55s, I'd be in trouble.

 

[fishn&huntn]

subsonic would probably not cycle an AR.+1 ON THE 1 IN 7

 

[DrBaker]

My personal experience has shown me that a 1:7 twist is good, including my SBR testing.

I shoot from 55-77gr in 5.56 and this has always worked in every 1:7 twist barrel I have used. The most common complaint I hear about the 1:7 twist is that it won't work with 55gr. I guess somebody somewhere might have problems with it, but I can't count the number of times I've successfully ran the combo. Never a problem with it.

On a side note- I've had a few 1:9 twist barrels that would stabilize 75gr. Not every one of them, but it can happen.


My personal choice after trying several bullet weights, twist rates, and barrel lengths is the 1:7.

 

[idleclamp]

I've heard that some can get the bolt to cycle and some can't. One person told me that 100 grainers shooting subsonic would do it. I'm trying to do a couple of things: 1. I want to be able to slow it down to subsonic without worrying about a baffle strike even if it doesn't cycle the bolt and 2. not be limited on what regular ammo I can shoot.

Does anybody shoot really heavy stuff out of a 10.5" 1:9?

 

[Josh-L]

If you are going to run a can on it absolutely do not get the 1-9.

 

[jstevens]

From what I have been told the 55 gr stuff does start to come apart, but it is after approximately 300 to 400 yards when using a 1/7, 1/8 twist. One of the rules on the 600 yard high power range at okcgc is nothing smaller than 69 gr. I have a 1/7 twist in my 9.25" barrel and the 55 gr stuff shoots fine, but I don't shoot more than 50 yards with it. Get the 1/7

 

[CAR-AR-M16]

I shoot nothing but 55gr out of both my 1/7 twist 12.5" & 20" rifles. I regularly shoot at 300yds with no issues. I do not see how you could say it would hold together at short range, but come apart at long range when it is spining the fastest at the muzzle.

 

[idleclamp]

It sounds like it will be a 1:7. Thanks for all the responses. Now if I could just find one that's not ridiculously over-priced.......