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CAR-15 grouping problems

rawhide54
Several months ago I bought a DPMS CAR-15 with the 11.5 inch barrel and 5.5 inch flash suppressor to make it legal. I hadn't had a chance to shoot it at over 25 yards until last week and it had always grouped three and five shot groups tight enough to cover them with a quarter. I got to shoot it on a 100 yard range last weekend and was shocked. I couldn't get anything like a reasonable group at 100 yards. I'm using 55 grain bullets and plan to see if there's a difference with 62 grain bullets next time I can get to the range. Has anyone got some insight on this? Will the bullet weight make a significant difference? Is the 11.5 inch barrel just not capable of stabilizing the 55 grain bullet at 100 yards? I'm baffled. My Bushmaster XM-15ES with a 20 inch barrel will group tight at 100 yards all day long.
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Comments

10 comments

Date Votes
  • tsr1965
    If your gun has a 1 in 7 twist, it will indeed favor a heavier bullet. The 1 in 7 was really meant for the guys who shoot service rifle, and use the heavy VLD 75-90 grain bullets. With the standard ball 55 grain ammo it will shoot 4-6 inches at 100 yards. With the real light 40 grainers, it might not even keep them on the paper. I bet you will like the 62's better, and if you can find some 69's better yet.

    Best
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  • perry shooter
    What are your expectations[?][?]This is not going to be a target gun I suspect a 5.5 inch flash suppressor is causing many problems I would look very closely ar the inside of this item and see if you can see any skid marks where bullet is touching the suppressor. Take the barrel off and slide a cleaning rod down the bore then look at the muzzle and see how far the rod comes from touching the end of the suppressor while turning the barrel in your hand The Rod should clear the bore by the same amount on all sides.
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  • Mobuck
    You're shooting a barrel less than a foot long and I assume, open sights which is 2 strikes against good groups.
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  • tsavo303
    my colt 11.5" with a pinned break would do 1.5-2" groups at 100yds ( i was using a scope) with 55gr
    It would not do 4" with 62 gr as it was 1-12" twist
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  • Horse Plains Drifter
    Very interesting, I have about the exact same weapon except it's an Oly. It shoots the same way and I haven't had time to work with it much.
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  • rawhide54
    I think mine is a 1 in 9 twist that is supposed to be able to handle most any bullet weight. I'll see how it does this weekend with 62 grain bullets.

    Checked. No skid marks or indication of problems within the flash suppressor.

    Thanks for all of the input.
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  • grumpygy
    Who made the 55gr you are using.
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  • rawhide54
    quote:Originally posted by dnelson457
    Who made the 55gr you are using.


    Winchester
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  • Mobuck
    At one time, I had a 10 1/2" AR flat top pistol. I would do a little better than 2" off a sandbag rest with a rifle scope mounted. This was with 55 fmj military type ammo. I got an offer too good to pass on and traded it for something more practical.
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  • 1911 Gunslinger
    Your DPMS CAR15 does indeed have the 1/9 twist which should work well with either 55 or 62 gr. bullets. You didn't mention the size of the group. Most rack grade AR's will only group in the 1 1/2"-3" range with decent ammo. Surplus ammo will usually make them open up especially the steel core 62's. There could be a problem with the barrel's crown, the short sight radius and mil-spec trigger pull could also be contributing factors.
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