Posted: 9/2/2012 7:55:39 PM EDT
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i built my 2nd ar and it shoots, ejects but wont grab another round when bolt comes forward. i tried everything! i checked gas tube placement, tried different carrier and bolts (eventhough i know youre not suppose to), i tried swapping out different lowers, i even took weights out of the rifle buffer. i bought the 24in .960 DPMS barrel off gunbroker, headspaced it when i got it and the both GO and NO GO seated fully in the chamber.... i know i wasnt suppsose to fire it like that but figured "what the hell, i didnt spend all the money and time for nothing"
other than the fact that it wont grab a shell on reload it works. i just have to pull the handle everytime i fire, if i was looking for a bolt action an AR platform wouldnt be my choice 
any who, if someone can give me some advice it would be appreciated. thanks folks |
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At first, my gut reaction was magazines, but I don't think it would feed when you manually rack it.
The problem you're describing in pistols comes from too much slide velocity, so I'm going to go with too much bolt velocity in the case. You said you removed weight from your buffer, but I'd do the opposite. Try getting a heavy buffer. Also check to see if your gas port is within spec. When it ejects, how does the brass act? Does it seem like its over gassed? |
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It sounds like it is short stroking to me. Take a magazine, and load a single round in it. Chamber it and fire. The bolt should lock back on the empty magazine. If not, you have yourself a short-stroking situation.
Sources of short stroking are not enough energy delivered to the carrier, too much energy sucked off by drag in the mechanism, too much energy taken up by extraction, too much energy taken up by the springs.
Not enough energy delivered to the carrier - Obstructed barrel port or front sight base, poor fit of the carrier key to the carrier, carrier key screws not tight, gas tube end or carrier key opening worn and leaky, carrier gas path obstructed, gas tube obstructed, gas rings gone, large clearance between tail of bolt and carrier; Too much energy sucked off by drag in the mechanism - Binding or rubbing carrier, binding recoil spring, carrier and hammer binding on each other or inadequate lube on reciprocating parts. You can feel this during manual cycling, both with the trigger released and with the trigger pulled; Too much energy taken up by extraction - Rough, sticky, or out-of-shape chamber, as evidenced by marks on cases and bent extraction rims. Ammo/chamber that make excess pressure, as evidenced by pierced, cratered, flattened, or lost primers, buttons of case metal extruded into the ejector plunger hole, case head growth in firing. Dirty chamber - clean with gun solvent, then lacquer thinner; Too much energy taken up by the springs - Extra power recoil springs and hammer springs can be too much to allow full cycling. Start with GI, and if they work OK, then play with stronger ones. |
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Quoted: thanks for all the advice folks. havent had a chance to shoot yet but i will respond with the outcome. how do i fix short stroking? i tried surplus USGI Okay mags, brownells mags and a 20 rd pmag tried all with cheap tula ammo, PMC bronze and pmc xtac 556. We'll need more info before we get to that. Do you have the ability to measure your gas port? |