James B, I' ll bet that you had your wad stuck in your barrel, It happens sometimes that the wad will plumb stop on you, while the shot will head on out, sometimes the only noticed difference is the report and crappy velocity, which sometimes isn' t much different at all. Then you chamber a second round, and you bulge your barrel, but the wad isn' t jammed well enough to stay put, so it flys out, and the rest of your second round comes out with it, making you think you didn' t have an obstruction.

Either that or you were shooting loads in your gun that you shouldn' t be, if it were me, I' d be to ashamed to admit to that though too.