16" 5.56 twist rates

[captnmo]

There's a similar thread, but not quite limited to a 16" barrel so I wanted to start a new one.

For 16" barrels, what are comparisons between the 7 and 8 twist barrel. I know the 7 twist will stabilize the heavier bullets. But what are the reasons of some high end manufacturers using the 8 (Larue) and others using the 7 (Noveske). With the Mark 12 using the 7, you'd think they'd go with a well-proven design. Yet they all seem to be getting good results. A lot of lower end, commercial carbines are doing the 9. Not to say that a 9 twist is bad, but it just seems to be a trend.

I know the quality of the rifle's manufacturing and bullet has a lot to do with accuracy. But with all other factors being constant, what are the manufacturer's decision points for a twist rate on a 16" barrel

 

[TheShooter]

Re: 16" 5.56 twist rates

I have a 16" 1/9 barrel AR that loves 77gr SMKs. By far the most accurate bullet in this rifle. This rifle throws 80g sideways.

I have a Rem 700 PSS 1/9 cut to 22" that shoots 80g SMKs sub MOA at 500 yards.

1/8" is popular as conventional wisdom says that is needed to stabilize a 77g bullet.

The military chose 1/7" to overspin the 62gr load. By overspinning you can get the bullet to tumble upon impact.

 

[Trigger Monkey]

Re: 16" 5.56 twist rates

The military chose the 1:7 twist to stabilize the longer and slightly heavier M856 tracer round.

 

[captnmo]

Re: 16" 5.56 twist rates

So are you losing anything by going with a 1:8 twist instead of a 1:7 for non-military use in a 16"? My assumption is that a 1:8 twist will give you the same accuracy with the right bullet out of a 16" barrel.

 

[Trigger Monkey]

Re: 16" 5.56 twist rates

You're not really losing anything by going to a 1:8 twist barrel, it will probably serve you equally as well as a 1:7 twist barrel, whether you plan to shoot 55 gr projectiles or 77 gr ones. IMO it comes down to which one you can get first that is in the desired configuration.

 

[captnmo]

Re: 16" 5.56 twist rates

So what's the worse that can happen by shooting a light pill like a 55 grain through a 1:7 twist barrel? Do you just lose accuracy by over-spinning?

 

[Drifter™]

Re: 16" 5.56 twist rates

I use a 16" Rainier Arms Ultramatch (Shilen blank) with 1:8" twist, and get excellent accuracy with factory 69gr and 77gr loads out to 600 yards. I rarely shoot lighter bullets from this barrel.

 

[BaileyMoto]

Re: 16" 5.56 twist rates

My mk12 (1:7 at 18") shoots cheap Hornady 55gr Training ammo (steel case) almost as well as it shoots the 77gr SMK's.

I'm not exactly the best behind the trigger, but this rifle almost shoots itself.

77gr SMK's at <span style="font-weight: bold">-->> 200 <<--</span> yards:

55gr Hornady Training at 100 yards:

 

[CK_32]

Re: 16" 5.56 twist rates

This is what I have been told..

1:7 was for putting people down and heavier bullets

1:8 was for competition custom barrels but will shoot heavy and light bullets

1:9 are more of the commercial factory AR's can shoot the lighter stuff but is usually favored behind the 1:7/8's

Correct me if I am wrong.

But that was my $.02