If the gun fires both barrels when you pull the front trigger this represents some mechanical defect inside. These guns were designed & built to fire either barrel first dependant on which trigger was pulled. This could represent a bad sear notch for the left lock & iot is jarring off from the recoil. I once had an old J Stevens Arm & Tool Co 12 double which would on occasion fire both barrels if you pulled the rear trigger first. Turned out it had worn holes in the sears for the pins & sometimes the sear tails would get together & lift both sears simultaneously. The right sear sat slightly higher than the left one so it never did it if you pulled the right trigger first.
It is noted that when Bell loaded up high pressure shells to the point he burst the barrels on a couple of old Parkers,one damascus & one steel, they both burst in the chambers, not down the barrel a ways.A flaw in the barrel or an obstruction can burst a barrel anywhere of course, but high pressures gets it in the chamber.
