I agree that it could be a loose gas key.
When I first got my Bushy in '99, I used to take the gas key off when I cleaned the weapon. I ended up putting too much lube on the gas key screws, and the gas key would come loose and cause FTFs after about 40 rounds.
I dried the gas key screws, used lok-tight or whatever its called, and no more FTFs for 2,000 rounds. I don't take the gas key off during cleaning anymore, obviously. It's not necessary.