Are you shooting subs or supers?,
As above, hard to diagnose over the internet, but sounds like the bolt isn't running all the way back with recoil. Not going far enough back to cock the hammer inside the trigger mech but going far enough back to skim a round from the mag. So when it runs forward, it pushes a round into the chamber and the partially cocked hammer drops on the round causing the lite strike.
Conjecture again due to online diagnosis, but possibly beveling the back of the bolt, removed the section of the bolt that was previously pushing the hammer back into cocked position?.
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