Best twist rate for 62 grain and 77 grain 5.56 mm ammo?

Discussion in 'The Firing Range (Firearms)' started by Grenadier, Oct 15, 2008.

  1. Grenadier

    Grenadier Yum! Staff Member

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    Got a question for those who shoot AR-15-style rifles...

    What kind of barrel twist will be best for the the 62 and 77 grain ammo?

    Right now, my Bushmaster XM15-E2S carbine has a 1 in 9" twist, that's supposed to be good for stabilizing a wide variety of loads. I'm sure that it will handle the 62 grain loads fine, but what about the 77 grainers? Would a 1 in 7" be good for 55 through 77 grain loads?
     
  2. sgtmac_46

    sgtmac_46 Senior Master

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    The 1:7 is better for heavier loads.......you need to decide what loads you are going to shoot, as the 1:9 or 1:12 are better for lighter bullets.

    1:9 is okay all around if you can't decide what loads you want to shoot.
     
  3. Grenadier

    Grenadier Yum! Staff Member

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    Thanks.

    I primarily shoot Winchester Q3131A 55 grain FMJ from my Bushmaster, which works great with the 1 in 9".

    I am, though, contemplating buying a separate upper, or maybe just the barrel, in order to accomodate the heavier loads.
     
  4. sgtmac_46

    sgtmac_46 Senior Master

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    Yeah, the super-fast twist of the 1:7 tends to play hell with really light loads......but nothing stabilizes a heavy load like the 1:7.
     
  5. Archangel M

    Archangel M Senior Master

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    Rule of thumb:

    Heavy loads 1:7

    Lighter loads 1:9

    Light loads in the 1:7 have a possible risk of separating the jacket from the core when "overspun".
     
  6. terrylamar

    terrylamar Blue Belt

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    1:8 twist in a match barrel is an excellent choice for 62 grain bullets, and a good choice for 77 grain bullets.

    1:7 twist is an excellent choice for 77 grain bullets and a good choice for 62 grain bullets.
     
  7. searcher

    searcher Senior Master

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    I am currently running a 1:7 for all of my loads in my M4. I am thinking I will get a 1:9 in my next rifle, itis going to be for some 45gr. loads. Seems to me like is is a matter of preferance. The more the twist the higher the spin rate which leads to more stability.
     

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