The empty case has long been ejected out of the receiver. Maybe a maladjusted extractor can slow the cycling enough the bolt lacks the momentum to go into battery?
Aside from using a trigger system never intended for a controlled feed, blow back rifle I believe it's a chamber issue. Dirty or tight chamber only partially chambers a round and this rifle will fire out of battery. I doubt you can pull the trigger fast enough to catch a cartridge partially chambered. The case wasn't gonna go all the way in anyway. Dirty/tight chamber? Slow cycling? Result is the same. I've not had an out of battery detonation since I aggressively polished my chamber and bolt rails.
This rifle uses controlled feed. The cartridge case slips up and under the extractor and is held in the recess on the bolt face from the time it's stripped from the magazine. Once the bullet itself gets into the chamber it's held tight enough against the face of the bolt that the firing pin can firmly strike the rim and detonate.
The angles of the rear of the bolt, hammer, and firing pin will all make contact with the bolt partially open. I've heard S&W has changed some of the bolt/firing pin design to help prevent this but the fact remains that the M16/AR15 trigger system will release the hammer long before the bolt is in battery. The hammer cannot strike the firing pin until the bolt is
almost closed. Almost ain't good enough.
-- Chuck