[Marlin 45 carbine]

what is gonna do better with this fast twist barrel? newbie to loading for this one, but old hand at '06, X39 and 30-30.

[rcmodel]

Anything from 45-50-55 grain to as heavy as you need to go.

A particular 1/7 barrel might shoot any of them best, including the light ones.

rc

[loadedround]

From past experience any bullet under 62gr will not stalilize properly at normal 223 velocities. Some 1/7" barrels may even prefer 69gr bullets. Any bullet weight 55gr or under will pattern, not group at 100 yds..

[Walkalong]

The heavy bullets will not stabilize using slower twists, but the light bullets will be spun plenty fast to stabilize using a faster twist than needed. Sometimes they will be accurate, and sometimes they won't. Many folks shoot the 50 to 55 gr bullets in 1 in 7 twist barrels with good success.

[rcmodel]

Any bullet weight 55gr or under will pattern, not group at 100 yds.. Thats not the case at all.
I have seen more then one 1/7 AR that would shoot sub-MOA with 45 & 50 grain varmint bullets.

You can under-stablize a heavy bullet with slow rifling, but it is darn near impossible to over-stablize one in a fast twist as long as it stays together long enough to get to the target.

rc

[Marlin 45 carbine]

ah yes, info I was needing. thanks to all.

[Win1892]

I shoot 1in7 and 1in8 uppers in the AR .223 platform, in 20" and 24" respectively. I can't get less than 62s to group well at all, with 45s key-holing or missing the paper completely. I think the short bullet length hurts you. I shoot 68, 75, and 77 with consistent 2.5" 5 shot groups at 300 yards. I do have to seat them very close to the lands for this accuracy.

[Mags]

Any bullet weight 55gr or under will pattern, not group at 100 yds.. My 16 inch 1/9 twist barreled AR and 55 grain Hornadys beg to differ.

[tlen]

SLUGS ?
http://www.shilen.com/calibersAndTwists.html

[loadedround]

Mags: I was referring to barrels with a 1/7 twist only. All of the lighter bullets will work with a 1/9 twist barrel or slower. I own two preban Colt AR's with 1/7 barrels tha won't shoot for beans with any load under 62gr. In the past I also sold a third Colt Hbar that would not group lighter bullets also. It is my understanding that the military load for the 1/7 twist AR's was the 62gr load. I don't remember offhand the military designation of this round.

[matrem]

SLUGS ?

A very common term for projectiles fired from guns, not just shotguns.

[Jim Watson]

The 7 twist .223 barrel is the Army spec to handle the very long M-856 tracer bullet.
It is good for 80, 82, and likely 90 grain boattail match bullets, seated long and loaded single shot; and plenty for the 77 grain magazine length bullets.
It will shoot M-193 55 gr FMJ and any light weight target or varmint bullet that will stand the spin. Some won't.
Accuracy is left for the student to test in his own gun.

[madd0c]

I have a 1-7" twist 16" barrel AR myself and went to the range today to answer this EXACT question :)

I shot 5 shot groups over a chrony with 55,62,69,72 and 77 bullet weights all seated to 2.25"

My short barrel AR seemed to like the 69gr bullet the best, but the loads I was using (23gr of IMR4064) was only pushing them at about 2400 FPS.

Seemed to group well though. Will work up toward max load and see how the accuracy is.