Finally got to try it.  It was with my SAR 1.  I think they were 3,4 or 5 round bursts at a time so I still need work on it.  Also I had a spent caseing nail my thumb, and of course I banged it 3 times since.  No Cops or Sheriffs called, but then again I was shooting with a bunch of them.  All in all a good day.

I would have tried my AR but I'm on ration mode.  The full story should be devulged in about 3 weeks from today.  I'm not sure, but I think I'm still sworn to secrecy.

After a little practice, you will be bumping off drums...
I did a 100 rounder "non-stop" last Summer...
My buddies thought I was a god...

The 7.62 AK's seem to be very user friendly whe it comes to bumpfiring...

When they are new, they're a bit tight and sticky, but after 1000 rounds or so, they are "loose as a goose"

Keep practicing...
Chances are, your thumb got nailed by the charging lever on the action cycling back, not a spent case...
I know this from experience...
I bloodied my thumb quite a few times 'till I finally got in the habit of folding it back...

Best advice is to relax and let the gun do the work...