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Posted: 7/20/2008 11:29:42 AM EDT
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I am running a bushmaster, gov't profile, 20 inch A2 upper on a preban bushmaster lower with a2 stock. Pretty much plain jane ... no extra doo dads except a mcfarland one piece gas ring. I rebuilt the upper from a 16" hbar to the now new 20" gov't. I took it out for the first time yesterday and fired it. I strips the 1st round off, chambers, and fires. The case looks fine upon review after ejection. Head space looks great. But it doesn't feed a 2nd round into the chamber. it either hangs up a thrid of the way coming back down, or it slams shut on an empty chamber. My friends dad ( nam vet and self proclaimed ar15/m16 nut) reviewed my parts and found that my bolt was VERY tight in the carrier. Upon inspection he noticed i had a 1 piece mcfarland gas ring on the bolt and it was just way to tight. He took the bolt and carrier completely assembled and held it upright in the air. With a chopping motion, while holding onto the back of the carrier, he swung down towards the ground quickly and brought the bolt/carrier upgright. he said if it were in spec, the bolt would have fallen forward into the locked positon. It didn't. Now when i was building the upper i put the mcfarland gas ring in for no reason. I had it laying around and assumed it was only beneficial. I trashed the old rings and now dont have spares. Do you think this could be the cause of my problems? Maybe the bolt cam pin is wedging itself in the upper prior to stripping a round ? Or the bolt isnt caming all the way prior to meeting a new round ? It's the only thing i can think of. ( PS i have built several AR's before without a problem. ) PS i have omitted the gas tube as the cause. EVERYTHING is lined up properly. Thanks |
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In before the "Bushmaster sucks" trolls chime in. Seriously, call Bushmaster. They'll have an answer for you. E-mail works great, too. You should be able to push the bolt all the way back into the carrier, then grasp the carrier at the end and swing it smartly and inertia should carrier the bolt all the way forward. At the same time, you should also be able to take the fully-extended bolt and place it on a table, vertically face down, and not have the carrier ride down. Have you tried different magazine? |
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With the bolt all the way forward in the carrier, at least confirm that the Carrier will slide down the Upper receiver track without the cam or sides of the key binding on the upper slot. As for the one piece ring, time to work the Bolt in and out of the carrier until it looses up a bit ( or just order a set of rings and install them instead). With the upper cleaned and CLP lubed correctly, load only a single round into a mag, insert the mag and charge the single round, then fire such round. The end result should be that the bolt is not locked back on the hold open catch. If the bolt does lock back, then the rifle is stroking correctly, and problems should be checked with the mags. |
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update... I removed the mcfarland gas ring from the newer bushmaster bolt/carrier and put it on a VERY loose tolerance bolt and carrier i bought used on the EE. STILL VERY VERY TIGHT. It is obviously the 1 piece ring. And i won't bash the mcfarland rings as i have one on my preban colt m4'gery and it works GREAT. I guess this ring is goin in the trash and i will be going back to plain good ol' 3 piece rings. I won't mess with something that isn't broken. Thanks all. |
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