I use to do the same thing with 45-70. You need to cut a 3x5 card to wrap around the .410 shot cup to make it fit just right.I poured in the shot and then put a 1/8" think piece of cork over it and then put a light crimp on the brass to keep it in.great for grouse.
Similar shot rounds can be made of just about any pistol cartridge uisng two gas checks with the shot in between. A lot of us older frats use to do that.Now I use the Speer shot cups and have no trouble dispatching grouse, even with a.357 snubby at 4 yards or so. Sure do hell on a mousei nside the tent at 3-4 feet though,but it sure makes a mess all over everything.
I suppose you are using large rifle primers since the 444 is a rifle cartridge.
