My rifle shot fine for the first 500-600 rounds, then I found that the gas plug had shot loose, and evidently allowed my piston to cause a small burr on the surface of the receiver side opening. I stoned the burr down and reassembled the rifle, and shot it several more trips. Latter on I completely disassembled the rifle for cleaning and to check to see if the problem was solved. Everything looked fine and I reassembled the rifle after cleaning. The next trip out the rifle would not cycle after the first shot, I can manually strip another round from the magazine and it will fire each time but not open the bolt.
My gas cylinder is unitized, the piston will move back and forth with gravity, and my op rod doesn't seem to be binding on anything with or without the op rod spring attached.
The only thing I have changed is that I have switched to LC brass with a slightly decreased load of IMR 4064 from what I had been successfully using in commercial Winchester brass. The cases did seem to have more soot on them than normal but I didn't really notice anything unusual that would lead me to believe it was ammo related. If I get home in time to day I am going to reassemble my rifle and try some factory Q3130 through it.
My only other thought is that my gas cylinder and barrel are out of alignment. I thought I would check here and see if any of my more experienced M14 brethren had any other ideas for me to try out.