black powder in shot shells????

I suppose 2 1/4 to 2 1/2 drams? 2 1/2 dram equivalents is common in 12 gauge field loads. They don't print the dram equivalents much on a box of shotgun shells anymore, but basically, it means that's the smokeless equivalent of a 2 1/2 dram black powder charge.

One dram is 27.5 grains. Try 2 1/2drams (68-70gr) of Pyro RS. Top that with a modern shotcup, before loading it put some stiff lube in the cusion part, 1 1/8oz of shot and crimp.
As a lube, try a 50/50 mix of Bore Butter and beeswax, or crisco/beeswax in the same formula.

Oneshooter
Livin in Texas

You may have trouble with total charge length, as 70 grains of blackpowder takes up a lot more room than a modern smokeless load. I've been loading BP shotshells for Cowboy Action for several years, this year I've cut my load back considerably due to powder and lead prices. I use a Lee 7/8 oz dipper of Pryo RS, one nitro card, two cushion wads and a 7/8 oz dipper of shot. This is my standard load for 16, 12, and 10 gauge.
Anyway, some plastic wads will require the shock absorber part being cut off, if you choose to use plastic.
Also be aware a lot of the plastic will melt in your barrel, as BP burns hotter. It cleans out easily, but is kinda surprising if your not expecting it.

If you decide to try some black, clean your shotgun very well before shooting to remove any smokeless residue, then coat the inside of the barrel with Bore Butter or Ballistol.

You may have trouble with total charge length, as 70 grains of blackpowder takes up a lot more room than a modern smokeless load. I've been loading BP shotshells for Cowboy Action for several years, this year I've cut my load back considerably due to powder and lead prices. I use a Lee 7/8 oz dipper of Pryo RS, one nitro card, two cushion wads and a 7/8 oz dipper of shot. This is my standard load for 16, 12, and 10 gauge.
Anyway, some plastic wads will require the shock absorber part being cut off, if you choose to use plastic.
Also be aware a lot of the plastic will melt in your barrel, as BP burns hotter. It cleans out easily, but is kinda surprising if your not expecting it.

If you decide to try some black, clean your shotgun very well before shooting to remove any smokeless residue, then coat the inside of the barrel with Bore Butter or Ballistol.

Forget the plastic, get you some high brass paper shells, use 70 grains of 2fg and you will be fine. IF you need to adjust for volume to crimp the shell, experiment with some cream of wheat on top of the BP, then the card. A lot of fun in a double barrel or single shot. DON'T use in an automatic, it will gum up, and then corrode the works real quick.

I shot some BP loads at the trap range an thought it was pretty funny no one else shooting had a sense of humor.