An AR15 problem

[Snake]

I bought a LNIB Bushmaster (It was a good price ok?)anyway It shoots good,is fairly accurate but it has one problem...It won't lock back after first shot. Heres what I've done to it so far...Swapped bolts with a known good one...Swapped buffer and spring with know good one...tried several different known good mags. No improvement. I've been shooting new Federal .223 55 gr. FMJ. As said It cycles fine just no last round hold open. Ideas?

 

[BrandonM]

Can you manually cycle the action with an empty mag and have it lock back?

 

[Snake]

Can you manually cycle the action with an empty mag and have it lock back?

Yes. Will do this with any mag I insert.

 

[dennishoddy]

Does it have an adjustable gas block?


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[Glocktogo]

Have you tried pulling the bolt catch out and checking for burrs or defects? Bushy's are usually overgassed, so even running 55gr .223 should be enough to get the bolt to lock back.

 

[Snake]

I think its a standard gas block. Has the standard A2 front sight. Have not checked the bolt catch. Think I will try that this evening. Thanks for the ideas...this is maddening....

 

[BrandonM]

Is it a carbine length gas system? Have you pulled out the buffer and spring to check those?

I’m thinking if it’s not magazine related it has to be a gas problem, bolt catch problem, or buffer problem.

How is the ejection pattern?

 

[dennishoddy]

Alignment of the gas ports can be an issue as well.


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[Snake]

Yes carbine length The buffer and spring are the right weight and length. The ejection pattern is about 4-5 o clock right into the brass deflector. Im hoping I can get this fixed with out having to take the front sight off and check the alignment.

 

[BrandonM]

I was just curious if it was throwing brass a country mile or dropping it at your feet. Weak ejection would be an indicator of not enough gas.