204Ruger

I've put together a 204 ruger ar-15. It's got an 18 inch Wilson combat barrel with match gas block and rifle length gas tube. The lower has a rifle length a2 style stock. The rifle will not cycle the next round and will not lock back after last round. Its throwing brass at about 3 to 4 o'clock. I've tried it on two other lowers and it does the same thing. I've also tried different buffers and the only way I can get it to run is to run a 3 ounce carbine buffer in the rifle tube which probably isnt right. So what could be my issue? Thanks in advance.

You may not be getting enough gas to fully cycle the BCG. This is the issue I had with my 6.5 Grendel build. After I broke the upper down and re-aligned the gas block over the the port on the barrel it cycled perfectly.

mY AR'S are all .223, my .204 is a bolt gun. sorry

Your gas block is not aligned or if an adjustable one, then set to low, for gas flow.

The gas block is a set screw with a pre drilled notch in barrel. Both barrel and gas block are wilson combat and it's not adjustable

I had a similar problem with mine not locking back with my AR-10's I put together that ended being a receiver issue. In my case, the problem would move when swapping receivers amongst the two I had at the time. One thing different though mine would cycle and pick up rounds. Since the problem tends to move with the specific upper and the lowers work on the other uppers that would point me to your upper that is giving you the problem and that the ammunition isn't the issue.

Could you be losing gas else where such as where the tube meets with the BCG?
Are you sure the gas port and the gas block are aligned?
Could the gas tube or the gas block be defective?
If it's an adjustable gas block back the adjustment screw all the way out and give it full gas pressure.

When I put mine together I drew a line along the barrel and the gas block across the ports to help visually to align them up, it worked pretty good too.

If I come up with anything else, I'll let you know...good luck.