JPS; I had an old 12ga J Stevens, 325 I think, that started doing that, but only if you pulled the rear trigger first. Turned out either the pin for the sears or the hole in the sears (Or both) were worn & let the sear tails rub together. The right one set just higher than the left so it never caught the other, but the left one would. Knocked the sear pin out, put a little coil spring from a ball point pen between the sears to keep them pushed apart & it never happened again. I used it for close to 10yrs after that I guess.
Miller
