Did a recent rebuild with a NM gas system and didn't realize that there would be cosmoline or grease in the gas cylinder so didn't clean it out. Get to the range finally and the gun fires once then won't fire the second time. Pull the bolt, extract the unfired round manually, let go the bolt, fires once, etc. Field stripped at the range, found all sorts of grease keeping the piston from sliding freely. Cleaned it out with what I had (rags, carb cleaner, etc) and it worked flawlessly. Oops. What a doofus. Oh well, I feel better now. Had fun shooting but my scope sucks so don't have any good tarkets to post. I'll probably be back again tomorrow so will try to get a nice target.