Since alot of people are getting into AR's the question always comes up on velocity loss with a short barrel. A while back I did a test using 6 different Colt guns with XM193 ammo. I know different ammo and powder may make a big difference but it gave me a reference to use. I found it the other night and thought someone might be interested.

14.5" 1/7 twist...3068 fps
16" 1/7 twist...3169 fps
16" 1/9 twist...3147 fps
16" 1/12 twist...3099 fps (old SP1 made in 70's,lots of rounds)
20" 1/7 twist...3275 fps
20" 1/12 twist...3279 fps

5 shots averaged on the Ohler chronograph at 12'
Notice from 16-20 the difference is just over 100 fps and from 14.5-16 the difference is also about 100 fps.
I shot 2 14.5" barrels that day but didn't know the twist of one so I didn't list it but the velocity was comparable.

Tom thanks for the post, You have added some info that I needed.

I have been concerned about dropping down to a 16". Other than the noise factor there won't be much difference. How do you think the 1/7 will handle a 55gr BT? Thats what I shoot dogs and hogs with down at the ranch. Im shooting a 1/8 in my RRA 18" and 1/9 in my LTR, they like the 55gr's real well. Thanks for the info..Don

Anything faster than a 1/8 will stabilize upto 69 grain bullets fine....I am unsure of the heavy 70's and even the 80's on what the minimum twist rate is.

Most 1/7 twist will handle the 77 grain down to the 50 grain bullets which is what I shoot 99% of the time. I have a 1/9 twist that handles the 40 grain up to the 69 gr bullets.

THX for the post Tom.
Kelly

My 1-8 twist bull barrel loves the 55 gr bullets.

Some people have had problems using anything heavier than 62 gr in a 1-9 twist, but each rifle is different, everyone has to find out what works in their rifle.

Very Very True