Strangely after letting it just sit on the bench for awhile I was able to get it unstuck by pulling back on the charge handle. So perhaps its getting caught on something while heating up?? Doesn't really make sense because I only put 30 rounds through it the other day at a slow pace with 3 shot groupings.
The key seems to be that it gets sticky and eventually perma-stuck only on the LAST round of each mag...any ideas?????