I received the op rod back recently. The piston was supposedly in spec at .5257", so he didn't replace it. I ran about 20 rounds through it today, and it fed the 2nd and 3rd round properly about 1/3 the time.
Any other ideas??
I loaded up 48 more rounds with 47.5 to 49 grains of Alliant Reloder 15, which functioned well the last time I tested it. If it works again, I'll likely try out some IMR 4320 or Accurate 2520. I'll settle on the fastest powder that reliably works.