The original powder for it was IMR 7383. Nominally it used 110 grains under an 827 grain bullet for 1745 FPS with 38,000 PSI max avg. chamber pressure. That's well within what ought to work well with a cast lead bullet. This powder from old pulldown .50 Spotter cartridges (and supposedly "new" powder from some dealers) is still available at $4/lb from several surplus powder dealers. I got some from Hi-Tech Ammo and note that they sell cases, primers and pull-down tracer/incendiary bullets from the spotter rounds as well.

I guess I should correct that about the 7383 being the "original" powder. It was the purpose-made powder specially for the .50 Spotter. The first rounds were loaded with IMR 4831, 120 grains nominally for 1850 FPS @ 35.000 PSI max avg.

I've thought this cartridge could be used to build a practical big bolt action rifle for the heaviest game.

John--It would work, but messy to clean barrel.For cast loads and less mess,maybe use a real slow surplus powder.Less expensive than pyrodex.Ed.

Thanks ED,I wasn`t worried about cleaning up,my handguard acts as a locknut on my gun, and i can take the barrel off in a couple of minutes,and change it,i`ve got 3 barrels for it, a 36" 50BMG,18" 50BMG,and a 22" 50 Spotter barrel,it`s a Ferret upper for thr AR15 lower,and a ball to shoot,more fun than my TC BIG BOAR 58,I USE A 600GR Wadcutter,and 140gr Pyrodex P powder,for deer hunting,and i`ve shot as much as 190gr of powder,using a 900gr wad cutter,puts it in the same class as a 458 win. John

Thanks for the info,but i have all that,i reload alot of spotter ammo,i was wanting to tinker around with some reduced loads in black powder,or pyrodex,for some fun shooting,i`am sending you a pic of my rifle..John