" . He experiences case expansion when
Yikes, If he's using the slowest burning grade of smokless, he'll blow his shotgun apart. Then he won't have to worry about case expansion anymore.
I would suggest you get a copy of the Lyman Shotshell Reloader guide and select a load from that book.
Ammunition reloading is not something to be done by guesswork. Listed loads have been pressure tested and are safe to use.
The only smokeless loads I've seen were in that Handloader's Digest article from many years back. You don't load shotshells like any other ammunition, you have to find a receipe and stick with it, no substitutions. A lot of shotguns are made on the lower end of action strength, you can easily escalate pressures above what they'll take with simple substitution of components. Mixing of smokeless powders at home with no pressure equipment is a good way to lose some appendages. The smokeless powders of the late 1800s were bulk powders, volume for volume equivalent with black powder. There are none of that type being made today and using the current dense progressive-burning powders that way is a good way to blow up a gun. Blackpowder(or one of the replica blackpowders) is probably the safest propellant to use with brass shotshells in the absence of pressure-tested smokeless data.
Now there's a shop project for you, build a pressure gun for shotshells.
Stan
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