Don't get me wrong, I still think that this is an incredibly bad idea, messing with the black magic that shotgun shells are made with, for a lot o reasons, but I've got a question or the people here. Popping one of them through a full choked shotgun- Would that be much different from running a standard round through a full choked gun with back-bore? Obviously, yes, there is going to be a huge difference in a lot of ways. Back boring loosens pressure at the barrel, it doesn't have to deal with the extra weight and size of the hull, it doesn't have to deal with the sudden "thud" when that oversized lump of lead and plastic hits the choke, but given the fact that the pressure at the choke is at the lowest levels that it could possibly be, is that even a true concern?
it still isn't a slug. at impact, that thing is very likely going to rupture or strip the crimped part, if it doesn't right at the barrel. Then you have nothing different than a close range hit from a regular shell, except for the unknown factors of fluidity of the shot.
after a whole lot of thinking, I have decided for myself, at least, I guess that it isn't extremely unsafe, but I'm not convinced. although it wont work as expected to, that it won't be in the least bit accurate, that there are still a buttload of problems, I don't necessarily think any more that it represents a serious danger to the shooter of a gun that isn't sensitive to it.
I'd not do it unless my life was in question, maybe not even then, because it's not meant to work that way, and considering how freaking picky shotgun loads are already, it bugs the heck out of me that someone is willing to jam an oversized, overweight, out of the normal powder and shot and shell combination through the cone and barrel of a shotgun.
Something that keeps coming to mind is all of the shotguns that were blown to kingdom come when people loaded the "new" wads with old wad loads. Back when, wads were disks of cork, paper, whatever, and a heck of a lot of gas slipped through as it jumped the shell gap and went through the process of the bore. Then, we came out with the obturating wad, a cup shaped paper wad that popped out to fit the bore and allowed no gas leakage beyond what slipped past the hull. Obviously pressure increased at the chamber and back end. Then, we came up with plastic wads that lost even less pressure, and when people kept using the old data, chamber and back end pressures were pumped up far beyond the old norm, and yes, a heck of a lot of ordinarily adequate barrels split. Pack a muzzle loader with a load meant for a smokeless shell, especially with a heavy, high power shell, and your' playing with fire. No leakage anywhere, smokeless loads through a BP proofed barrel, we did a lot of really dumb things in the past without knowing better, and this sure seems to be a similar situation.
The OP didn't say that he planned on trying it, but still, I sure don't like the idea and would caution anyone contemplating it to think twice.
