The problem with 45-70 cases is that they are tapered. I used to load 45 colt shot loads with 2 gas checks (1 over the powder, shot and 1 to seal the mouth of the cartridge) but found that the pattern was real "holey" so I cut down 410 plastic wads (worked much better). But as I said the tapered case causes a problem here (lack of a gas seal) as will the rifling . I guess you could put in the powder (small amount of pistol powder) then wad up some paper and pack it on top of the powder then add a plastic wad, shot then place a piece of thin cardboard over the shot and hold it in place with a dab of hot glue or silicone caulk. I've had less than impressive results with rifled barrels and shot loads, mostly donut shaped patterns. Good luck.
