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1:7 twist in 5.56x45

Discussion in 'Rifle Country' started by Brad5192, Oct 26, 2008.

  1. Brad5192

    Brad5192 Well-Known Member

    I have a colt ar-15 with a 20" barrel and a 1:7 twist what is a good bullet for out to 600yd.
  2. cbrgator

    cbrgator Well-Known Member

    77gr match grade
  3. esmith

    esmith Well-Known Member

    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.
  4. Tarvis

    Tarvis Well-Known Member

    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.
  5. Float Pilot

    Float Pilot Well-Known Member

    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.
  6. SimpleIsGood229

    SimpleIsGood229 Well-Known Member

    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.
  7. Brad5192

    Brad5192 Well-Known Member

    Thank you all
  8. esmith

    esmith Well-Known Member

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

    RockyMtnTactical Well-Known Member

    Anything from 68gr OTM to 77gr OTM should work great.

    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...
  10. esmith

    esmith Well-Known Member

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

    RockyMtnTactical Well-Known Member

    No. It shouldn't be a problem. I've never seen any of the lighter bullets keyhole out of my 1/7.
  12. taliv

    taliv Moderator

    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.
  13. skinewmexico

    skinewmexico Well-Known Member

    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.
  14. Walkalong

    Walkalong Moderator

    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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