Originally Posted by
Ballistics in Scotland
There isn't much danger in this kind of reloading. Long before pressures become dangerous, you would get unacceptable shot patterns, through excessive muzzle pressure or shot fusing together.
The first gun I ever owned without air coming into it was the Webley 9mm. rimfire shotgun. It gave pretty good patterns with only a single-layer moulded cardboard cup wad, open end facing rearwards. I don't think calibers like this are nearly as sensitive to quality of wadding as larger shotguns.
I'm doubtful about the use of gas-checks. The pattern is liable to pass around the one at the front, and the one at the rear won't be left behind as quickly as a lighter one. I'd be more inclined to use card or waxed felt. If a wad punch doesn't cut cleanly enough (which one sharpened to a thin edge should), spinning the punch in a lathe or a drill-press should do so. A lathe or a drill with a hole down the spindle would let you knock it out with a metal rod. Over the shot I would use a thinner, frangible card sealed with wax.