Two years ago I bought a 458 socom upper on a RRA receiver. I interrupted subsonic load development to remove the barrel and profile it for a homemade silencer. When I resumed load development, I noticed that the brass did not come out black with bullet lube like they did before I removed/replaced the barrel, but did not attach any importance to it. I also was not able to make up a subsonic load with bullets up to 515 grains that would extract, not even with the buffer emptied of its lead weights and the spring cut down to a strength barely able to feed reliably.

After e-mailing Marty, I tried RE7, but this did not help. He also suggested that I check the front sight alignment. I checked the radial alignment, but not the linear, until today. I had re-installed the front sight about 0.025 inches too far forward, blocking about 25% of the port. I installed the front sight properly. With full gas flow restored the brass extracts dirty again and the action functions normally with the stock spring and buffer.

The more I know, the more I find I don’t know.

Ranb