Dies for .50 Remington Pistol available from Buffalo Arms USA for $142.00 USD. (CH4D- maker)
Accurate Molds can supply a bullet mold of just about any size.
Their catalog lists #51-285E that would work well (RNFP) 285 grains of wheel weights, measuring .512" dia. (Iron, alum., brass options)
Heavier cast of pure lead, which it should be.
The article mentions that neck-reaming may be necessary for short cases based on the .50 rifle brass cases, in order that the neck external dimension not be too thick on loaded rounds.
Mainly you cut the cases down, file the ends smooth, and then use a case trimmer to finish to length, and chamfer.
It also warns that bore size can vary, so you would need to slug your bore and measure the result to decide on your ordered bullet mold diameter.
A chamber cast would probably be wise to confirm the actual length and diameter of cartridge needed.
An unreamed dummy round would tell you if the round would chamber without reaming, I think.