1:7 twist in 5.56x45


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Brad5192
October 26, 2008, 03:37 PM
I have a colt ar-15 with a 20" barrel and a 1:7 twist what is a good bullet for out to 600yd.

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cbrgator
October 26, 2008, 03:46 PM
77gr match grade

esmith
October 26, 2008, 03:54 PM
Bullets of the heavier variety will perform better in a tighter twist rate, bullets of a lighter variety will perfrom better in a twist rate that is slower. 1 in 7 is of the faster variety so grain weight from 75 to 90 will perform the best.

Tarvis
October 26, 2008, 04:43 PM
grain weight from 75 to 90 will perform the best
I'm not 100% positive, but I think you can go lower than 75gr. and have good results.

You could try a 69 gr smk.

Float Pilot
October 26, 2008, 04:55 PM
The 55 grain M-193 and 62 grain M-855 ammo work fine in the 1 in 7 twist as well. But,, those projectiles start loosing out past 400 meters compared to the longer and heavier slugs. I shot some pop-ups at 700 meters ( machine gun range), with M-193 ammo and about 30% of them were keyholing. The M-855 green tip did much better with only a few showing some yawing. I fired both from a 1 in 7 twist weapon.
The 1 in 7 twist was not needed for the 62 grain green tip ammo, but rather for the longer new tracer rounds.

The 77 grain match slugs really shine in the 1 in 7 twist.

SimpleIsGood229
October 26, 2008, 05:27 PM
Black Hills Mk. 262 (77 gr. SMK). This is loaded to 5.56-level pressure, as opposed to the SAAMI-spec, .223 commercial Black Hills loads.

Brad5192
October 26, 2008, 08:58 PM
Thank you all

esmith
October 26, 2008, 10:03 PM
I'm not 100% positive, but I think you can go lower than 75gr. and have good results.

You could try a 69 gr smk.

They will work, but when shooting out to longer ranges they may keyhole.

RockyMtnTactical
October 26, 2008, 10:26 PM
Anything from 68gr OTM to 77gr OTM should work great.

They will work, but when shooting out to longer ranges they may keyhole.

No they shouldn't keyhole. That is a more common trend with heavier bullets used in slower twist rates... 55-62gr bullets should work just fine, although they lose more velocity faster at longer distances...

esmith
October 26, 2008, 10:31 PM
No they shouldn't keyhole. That is a more common trend with heavier bullets used in slower twist rates... 55-62gr bullets should work just fine, although they lose more velocity faster at longer distances...

I thought that since the twist rate was the fastest it would overstabilize the bullet causing it to wobble. Isn't that keyholeing?

RockyMtnTactical
October 26, 2008, 10:34 PM
No. It shouldn't be a problem. I've never seen any of the lighter bullets keyhole out of my 1/7.

taliv
October 26, 2008, 11:18 PM
esmith, no.

your earlier statement was technically correct but misleading.

any bullet may eventually keyhole. if it flies long enough to go trans-sonic, it can start to wobble. for example, my 168g SMK go through 1000 yrd paper sideways but make perfect circles at closer ranges.

the misleading part is that it is not because it's overstabilized and it's not unique to lighter bullets. however, lighter bullets typically have worse BCs and will go subsonic sooner.

skinewmexico
October 27, 2008, 12:27 PM
I have a Savage Model 12, but I've been really happy with how the Black Hills 77g SMKs shoot in mine. Hand loaded some 80g Amaxs that shot well too. Need to load the 80g Bergers.

Walkalong
October 27, 2008, 01:37 PM
Understabilized bullets keyhole. (too slow a twist for the bullet length)

Overstabilized bullets lose a little accuracy and a touch of velocity. (faster twist than needed for the bullet length)

All bullets, if they fly far enough, can lose enough spin to keyhole.

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