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03-29-2021, 02:43 PM
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Smith & Wesson M&P15 Sport II M-LOK .223/5.56 AR-15 Rifle 10305 30+1 16 Ammo
I purchase the Sport II yesterday and wanted to know if there are specific recommendations on what rounds to us in this firearm.
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03-29-2021, 03:16 PM
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Your rifle has a 1:9 barrel twist, so don't expect great accuracy with anything over 55gr. Basically the faster the twist, say 1:7 in an AR, the better the accuracy with heavier bullets (62gr or heavier).
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03-29-2021, 03:22 PM
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Quote:
Originally Posted by p8riot
Your rifle has a 1:9 barrel twist, so don't expect great accuracy with anything over 55gr. Basically the faster the twist, say 1:7 in an AR, the better the accuracy with heavier bullets (62gr or heavier).
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Emphasis on "heavy". 
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03-29-2021, 03:33 PM
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No firm rule on this. Try all you can. I get every good accuracy in a 1 in 9" CZ barrel using 65 Sierra GK and 69 MK. The 68 Hornady Match also does well.
Last edited by rockquarry; 03-29-2021 at 08:20 PM.
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03-29-2021, 03:36 PM
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No firm rule on this. Try all you can. I get every good accuracy in a 1 in 9" CZ barrel using 65 Sierra GK and 69 MK. The 68 Hornady Match also does well. Conversely, a couple of Colt ARs with 1 in 7" barrels shoot 55 grain bullets as accurately as they do heavier ones. I'm talking about good quality bullets here, not cheap bulk stuff that usually doesn't shoot real well in anything.
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03-29-2021, 03:44 PM
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Quote:
Originally Posted by rockquarry
No firm rule on this. Try all you can. I get every good accuracy in a 1 in 9" CZ barrel using 65 Sierra GK and 69 MK. The 68 Hornady Match also does well. Conversely, a couple of Colt ARs with 1 in 7" barrels shoot 55 grain bullets as accurately as they do heavier ones. I'm talking about good quality bullets here, not cheap bulk stuff that usually doesn't shoot real well in anything.
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Yes I should've made that distinction
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03-29-2021, 07:48 PM
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Quote:
Originally Posted by p8riot
Your rifle has a 1:9 barrel twist, so don't expect great accuracy with anything over 55gr. Basically the faster the twist, say 1:7 in an AR, the better the accuracy with heavier bullets (62gr or heavier).
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100% incorrect.
Original M16 twist was 1-12, and quickly changed to 1-11. When the M16A2 was fielded rate was changed to 1-9 specifically to stabilize the longer 62 gr steel tipped SS109 projectile.
In general 1-9 will work up to 70 grs, with 1-7 needed if you want to go to 77 gr.
BUT sometimes going that fast will cause issues with light bullet loads, such as 50 or 52 gr bullets. It is possible to overspin a bullet and cause longer range instability isses.
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