Was the barrel clean when you started? Might have been a fouling shot. I've noticed something with my pellet gun. If I lube the barrel and fire a shot I get 1100 fps velocity. The very next shot will drop down to 850 fps, and that's pretty much where it stays. Wouldn't be surprised if the same kind of thing happens with firearms, but I've never checked it on the chrono. JATCannot figure out why one shot in the 8-ring.