Twist Ratio

[Jader]

Hello all,

I am looking to build a new ar-15. So far I have a lower from PSA. I am running into a problem trying to decide what spin ratio I want for my upper. After looking through PSA's uppers, I noticed they only have 1:7 twist ratios. My question is... if I plan on shooting 55g bullets here in Colorado... will that twist ratio be too much? Also, what kind of range are 55g bullets accurate to?

[cstone]

Not a benchrest or precision round, but most will be as accurate as you are out to 500 meters. I don't know about you, but I can't see anything very well without good magnification at 500 meters.

55 Gr is a standard plinking round. Want more distance go 62 Gr or handload for your gun by working up loads at different weights.

Be safe.

[Jader]

What twist would shoot a 55-62gr the best?

[Colorado Osprey]

The Mil-Spec crowd will insist on a 1:7

That said, the most common is a 1:9.

1:12-1:14 will stabilize most bullets (35-63 grains) in a 223/5.56 with the exception of the heavy for caliber bullets like those VLD's made for very long range (69-90 grains) and the long for weight bullets like military tracer rounds.
1:9 will stabilize most bullets up to 75 grains (except tracers)
1:8 will stabilize almost everything (very few exceptions)
1:7 will stabilize them all but giving up velocity due to the higher spin and some lighter weight thin skin varmint bullets come apart before ever reaching target at distance. This has been well documented with v-max bullets.

With all that said I have no use for tracers so I don't own a 1:7. I do however own mostly 1:9's and a few 1:8's. For long range shooting for bullet weights up to 80 grains I have a custom built upper with a 1:10 which shoots sub MOA with 80 grain and under bullets from a 20" barrel.

[ray1970]

Colorado Osprey said it best. Unless you plan on shooting a lot of heavier bullets or tracers the 1:9 twist will work just fine. You can usually find the 1:9 twist barrels a little cheaper than the 1:7 as well.

[20X11]

IME...twist rate goes hand in hand with barrel length. 16 or shorter barrel doesn't stabilize 62 gr or larger bullets well in 1:9 twist. YMMV

[Jader]

I plan on getting a 16 inch barrel, which is standard I believe. Would a 1:7 barrel over stabilize a 55g bullet and effect accuracy?

[20X11]

I plan on getting a 16 inch barrel, which is standard I believe. Would a 1:7 barrel over stabilize a 55g bullet and effect accuracy?
No

[ColoWyo]

I would go with a 1-8. I really think its the best "all around" twist rate.

I've shot everything from 50 grain varmint loads to the 80 grain SMK's with good accuracy. That's out of a 20" RRA.

[MarkCO]

1:8 is the best all-around. I've witnessed the gray puffs of exploding bullets from 1:7s and lighter bullets. I've had no issues with the lightwieght varmint bullets in the 1:8s and have shot up to 77s at 1 MOA or better.

[Jader]

Thanks everyone for the insight

[SideShow Bob]

Now that you are decided on a twist rate, are you going with a carbine, mid length or rifle length gas system ? Just thought I would throw some more confusion at you..........[Coffee]

[G__Fred]

So SSB,

What are the Pros / Cons of each?

:Cool: