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Posted: 12/20/2010 3:56:53 PM EDT
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A friend recently brought me a stock Bushmaster AR-15 for cleaning (I know he should be responsible and clean his own, but I would rather a partner field a functioning rifle on duty rather than an unreliable one). The rifle reportedly had less than 1K rounds through it.
On my initial inspection (before cleaning) the gas rings tested good. I tested them by pulling the bolt forward in the carrier then standing the BCG on the bolt face. After I cleaned the rifle (and boy did it need it!), the gas rings failed the same test. The bolt was so loose in the BCG that it would easily move back and forth as I gently shook the BCG. I was surprised to find this in a rifle with less than 1K rounds. I took the rifle to the range. It fired the M-193 ammo okay, but, as expected, short-stroked on lower quality ammunition (Wolf). I suspect the short stroking was from worn gas rings. After about 200 rounds, the gtas rings tested okay before cleaning, but bad afterwards. I assume the only reason they are testing good before cleaning is because the carbon build-up is filling the open tolerances. I am surprised that the gas rings can be so weak after so few rounds, especially on a name like Bushmaster. I do not blame poor quality ammo, because I thing a duty rifle should be able to fire anything for a while. Am I missing something? Is there a reason for this? Thanks for the info. |
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Maybe the original gas rings were not up to spec.....
Gas rings wear out. Maybe the interior of the bolt carrier is slightly large 
Try and install some known quality gas rings or even a McFarland one piece ring to see if it stays tight in this bolt group............ |
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Ring test is push the bolt all the way in without the cam, them point bolt face straight down. If the bolt falls out, then the rings are worn out.
Bushmaster barrels are chambered on the tight side(cross wall dimensions), and may not do well with the coated ammo, even if powered on the hot side. If you suspect that the rifle is short stroking, then check the key allen bolts to confirm that they are 37 in lbs tight, and not either loose, or one of them having the threads snapped off at the head (head just retained in the key via the staking). As for the ammo, It's the M-193 that is loaded on the hot side(Nato standards), with the 223 wolf just loaded to SAAMI standards. Note: if you have 1/9 or faster twist barrels, then you may be better off with M-855 ammo instead. M-193 is still being used since there are 1/14 barrels still out there, and they will not stabilize the M-855 correctly. |
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