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Thread: Rifling twist on an AR?

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    Team GunsNetwork PLATINUM 10/2012 rci2950's Avatar

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    Rifling twist on an AR?

    So i am going with an M4 style in my build and will be either going with a 14.5 inch or 16 inch barrel. Anway i am seeing 1:7 twist and 1:8 twist but i thought 1:9 was the best for the standard 55 grain bullets... Whats the deal? The only 1:9 barrels i am seeing are full length rifle barrels.

    Second question, How hard is it to install a sight block on a virgin barrel?
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  2. #2
    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by rci2950 View Post
    So i am going with an M4 style in my build and will be either going with a 14.5 inch or 16 inch barrel. Anway i am seeing 1:7 twist and 1:8 twist but i thought 1:9 was the best for the standard 55 grain bullets... Whats the deal? The only 1:9 barrels i am seeing are full length rifle barrels.

    Second question, How hard is it to install a sight block on a virgin barrel?
    I believe 1:7 is nato standard to stabilize the longer tracer rounds. 1:9 is probably fine for 55gr and 62 gr. A lot of guys use 1:8 (which is am told often isn't actually 1:8 and is more like 1:7) and shoot 69 and 75 gr match bullets with it.

    IMHO 1:7 would be fine.

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    Administrator Krupski's Avatar

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    Quote Originally Posted by rci2950 View Post
    So i am going with an M4 style in my build and will be either going with a 14.5 inch or 16 inch barrel. Anway i am seeing 1:7 twist and 1:8 twist but i thought 1:9 was the best for the standard 55 grain bullets... Whats the deal? The only 1:9 barrels i am seeing are full length rifle barrels.

    Second question, How hard is it to install a sight block on a virgin barrel?


    My "genuine" Colt AR-6520 has a 1:7 barrel and the rest (Bushmaster) are 1:9.

    The 1:9 rifles are consistently more "repeatable" (i.e. smaller groups) than the 1:7 twist (using standard 55 gr ammo).

    As far as installing your own front sight block... don't even think about it. It's way too easy to screw up.

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    Contributor 02/2014 FunkyPertwee's Avatar

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    You'll appreciate the 1 in 7 twist for it's ability to use heavier loads. It handles 55 gr absolutely fine, just don't go any lower than that. M-193 ball and similar ammo will shoot just fine in it.

    About barrel length, go for the 14.5 if you're using a carbine length gas system like a real M4 uses. If you want a 16" barrel than use a mid-length gas system. I suggest the 14.5" so you can tease us with you're appropriate for an M4 barrel length (we have to use 16" down here).
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    Senior Member Partisan1983's Avatar

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    I wish there were more options for the original 1-14" twist
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    Forum Administrator Schuetzenman's Avatar

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    1 in 7 as Pots said was / is for the 62 gr. tracer round which is as long as the M80 147 gr. .30 cal. projectile used in 7.62 NATO. 1 in 8 is often exactly 1 in 8. Kreiger Barrels version is 1 in 7.875". 1 in 9 will do up to 69 gr. weight bullets and is a lot easier on the lighter cheaper usually M193 type 55 gr. bullets. 1 in 8 will stabilize up to the 80 gr. Sierra Match King bullet. 1 in 7 will also stabilize the 80 gr. Sierra and even heavier. 1 in 7 for 55 gr. and lighter bullets can (I've seen it happen) cause jacket separation in flight. Too many RPM's on the bullet can rip the jacket off and explode the bullet in flight. Will never happen with 1 in 9, you can't get the projectiles going fast enough to do it.

    Unless you're shooting 77 gr. and up bullets 1 in 9 is your best all around twist IMO. Now your short M4 barrel will not yield the speeds fast enough to cause the 55 gr. bullet to blow apart, I forgot to mention only seen this on 20" length barrels.

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    Senior Member NAPOTS's Avatar

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    Schuetz have you seen that with fmj? I know mountains of m193 have been shot through m16a2s with 1/7 barrels without issue

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    Forum Administrator Schuetzenman's Avatar

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    Quote Originally Posted by NAPOTS View Post
    Schuetz have you seen that with fmj? I know mountains of m193 have been shot through m16a2s with 1/7 barrels without issue
    Yeah I saw it with 55 gr. fmj rounds. Not sure if it was stock ammo or the guy was handloading. But his rounds were blowing up in flight around 200 yards out. Not everyone of them, just maybe one out of 10.

  9. #9
    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by Schuetzenman View Post
    Yeah I saw it with 55 gr. fmj rounds. Not sure if it was stock ammo or the guy was handloading. But his rounds were blowing up in flight around 200 yards out. Not everyone of them, just maybe one out of 10.
    Going off of memory because is been almost 17 years now we practiced with m193 and qualified with m855 shooting out to 300m. I remember being told the reason was that the m193 was cheaper and the m855 was more accurate and what the sights were calibrated to.

  10. #10
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    If anyone cares, I've seen a 16" 1/9 twist Olympic arms barrel shred 45 gr varmint hollow points years ago. My friend gave me some winchester 45 gr ammo when I bought the rifle and we went to go shoot it. Looked like bird shot on the paper at about 50 yards. We were both like wtf? Maybe the jacket of the rounds were super thin. Never seen it since.
    Now days I rock 1/9 and 1/8 twist rates and nothing below 55 gr. Usually m193, and m855, what I buy in bulk. Stash some and shoot some. On gas blocks I've put 2 on with no problems. One on a Bushmaster, and the other on a LR308 ap4. Maybe I got lucky. YouTube should have vids on that. Good luck with your build man.

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