I see discussions about shot loads in a double shifting in the unfired barrel, and the impression is that this would cause a dangerous situation. I don't think that's the case. With a standard shot column of powder, overpowder card wad, cushion wad (or not), shot and overshot card, the space between the overpowder wad/wads and the overshot wad is completely filled with shot. Think about what would happen to such a shot column under the effects of recoil. Things at rest want to stay at rest, so as the gun moves backward, the shot column wants to move forward. Physics tells us the heaviest parts of the column will resist moving backward the most, so the shot is the part which wants to stay where it is, in effect moving up the bore. The powder and the overpowder wad/wads, if properly snug, are not at all likely to move, too light weight, so not enough inertia, and tight in the bore if properly fitted, so too much friction to move. The overshot card won't have enough weight to move on its own, but it might if its friction is too little to resist the force of the shot trying to shift forward.
Friction of the wads against the barrel is usually high enough to prevent anything moving. If it isn't, think what will happen. The powder and overpowder wads stay in place, the shot moves a bit up the bore pushing the overshot card in front of it, then stops. Now the space between the overpowder and overshot cards is larger than required to contain the shot, so, with the barrel horizontal, the shot settles to the bottom of the bore, leaving a space above it. If you now fire that barrel, the overpowder wads moving forward won't hit a solid block of shot, but loose shot settled to the bottom. The expanding gas will escape over and/or through the shot, push the overshot card aside and escape harmlessly up the bore. It won't be like a solid obstruction with space between it and the powder, a situation which we know is dangerous. That might happen if you were loaded with ball, but it won't if you are loaded with shot.
I've been aware of having a load shift only once in all the years I've been shooting double shotguns, and I fired it without knowing it had happened. It was a really weird sensation. There was zero recoil from a fairly heavy charge of powder, and the sound was hollow, sort of a whoosh and an echo at the same time, hardly a real bang, at all. I knew immediately what had happened, just from the way it reacted.
In his book, "The Art of Shooting Flying", 1767, Thomas Page discusses this. He was using folded brown paper for wads, not cards as we do. I've tried his method, and the wads were not at all tight.
"After some experience you will find, if your gun is clean, and the wad thrust but lightly down, that in walking the shot will be apt to get loose: and if you discharge the piece in that state, it will seem, by the small resistance it makes as if there were no shot in it:"
Spence
Friction of the wads against the barrel is usually high enough to prevent anything moving. If it isn't, think what will happen. The powder and overpowder wads stay in place, the shot moves a bit up the bore pushing the overshot card in front of it, then stops. Now the space between the overpowder and overshot cards is larger than required to contain the shot, so, with the barrel horizontal, the shot settles to the bottom of the bore, leaving a space above it. If you now fire that barrel, the overpowder wads moving forward won't hit a solid block of shot, but loose shot settled to the bottom. The expanding gas will escape over and/or through the shot, push the overshot card aside and escape harmlessly up the bore. It won't be like a solid obstruction with space between it and the powder, a situation which we know is dangerous. That might happen if you were loaded with ball, but it won't if you are loaded with shot.
I've been aware of having a load shift only once in all the years I've been shooting double shotguns, and I fired it without knowing it had happened. It was a really weird sensation. There was zero recoil from a fairly heavy charge of powder, and the sound was hollow, sort of a whoosh and an echo at the same time, hardly a real bang, at all. I knew immediately what had happened, just from the way it reacted.
In his book, "The Art of Shooting Flying", 1767, Thomas Page discusses this. He was using folded brown paper for wads, not cards as we do. I've tried his method, and the wads were not at all tight.
"After some experience you will find, if your gun is clean, and the wad thrust but lightly down, that in walking the shot will be apt to get loose: and if you discharge the piece in that state, it will seem, by the small resistance it makes as if there were no shot in it:"
Spence
