How much does it pop out by? Barely out of the feedneck or a foot+ into the air?
That could be enough to cause you issue. How does you bolt fit on the guide? Does it fall right off if you turn it upside down? If it it too loose on the o-rings that could be the issue. But more likely you can cure it by using the fragile paint o-ring that came withthe bolt. Remove the rear o-ring and replace it with that o-ring and set your dwell to about 8.5 ms and see if the blow back goes away.
It doesn't fall right off, I have to shake it off.
Ok, putting on other O-ring..
And putting dwell to 8.5 (34 blinks)
Now going to shoot...
And same thing
the 2nd ball pops out literally just enough for it to pop out, I looked a little closer, and its probably a few millimeters
I would change all three. The o-ring you removed was noticably smaller the the larger one you put on the rear of the bolt, correct?
PM me and I will hook you up a little cheaper then normal since you are prt of the Simonized family.