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Posted: 3/18/2006 8:24:01 AM EDT
I just test fired two new builds. The first one ran fine but the second one won't pick up a second round. It cycles fine but won't pick up the second round. If I operate it by hand it will pick one up but not when I fire a round.

I tried several mags and got the same problem each time.

Any ideas?
Link Posted: 3/18/2006 8:30:00 AM EDT
Sounds like it's short stroking to me. It's ejecting the fired round, but not going back far enough to strip the next round.
It could need to be cleaned/lubed, or normal break in. On some other threads, some have mentioned the gas port being misaligned too, might want to check that.
Link Posted: 3/18/2006 3:18:11 PM EDT
It's short stroking. It might just need to be broken in. Try running the bolt carrier pretty wet with CLP for a couple of hundred rounds. If it still persists, then you need to find the cause of the short stroking.

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.
Link Posted: 3/18/2006 3:51:45 PM EDT
You're dead right on the short stroke. I gave everything a good clean up and I can see that the park is very heavy on the BC. It was dragging pretty bad. I degreased everything and reapplied break free. I can feel the difference just working the action. I'm going to run some hot loads thru it and break it in.

Thanks for the feed back. I should have know what the problem was. I was too pissed off to think straight. Some times you need someone to point out the obvious.

Thanks

Link Posted: 3/19/2006 8:14:50 AM EDT
With just the bolt carrier, and upper, you should be able to make the bolt carrier slide forward and back by tilting the upper. It should slide freely. Sounds like you just need some break in.

OR do you find a spot where there is a bind?
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