18 or 20" SPR barrel?

[CM1021]

I'm building another AR and I'm wanting this to be a somewhat long range rifle(read 500 yds). So I have been looking a different barrells and i think I'm gonna go with the white oak armament SPR barrel with a 1/7" twist...i will be feeding this rifle 77gr SMK and 69gr bullets and maybe some others to see just what it likes...so what's your guys opinion? Should i go with the 18 or 20" barrel? Also is it plausible to get out to 6-700 yards with an 18 or 20" AR?

[Dolomite_supafly]

Go with the longest barrel you can to take advantage of the heavy bullets and 7 twist.

I think you would be better suited with an 8 twist than a 7 twist. 8 Twist will shoot everything you can feed from the magazine, including the 77's. It can also shoot lightweight varmint and target bullets.

7 twist on the other hand cannot shoot some of the lightweight varmint bullet or some target bullets. I know a 53 grain SMK will come apart at about 3,300 fps in a 7 twist gun. And I am pushing those well beyond that in a 20" AR. 40 grain V-Max bullets come apart in my 7 twist at 3,300-3,400 fps.

But if you know you will never shoot anything under 55 grain then by all means get a 7 twist but a 8 twist will be better.

Dolomite

[CM1021]

Well I won't ever shoot anything less than a 55gr bullet but I may see if they have a 1/8" twist dolomite.