I've been casting my own Maxi-balls for my .45s for years.
I use a mixture of one lb Crisco to one block of "Gulf-Wax" (canning wax).
Melted and poured around the standing bullets, this hardens and I use a .45-70 case as a cookie-cutter to cut them free. I'll store them in stoppered, plastic tubes to keep them clean.
For .50s, you might use a .50 cal cartridge... the bullets will stay inside the case, once you've cut them free, but I push them out with an allen-wrench through the enlarged primer-pocket hole.
Sounds complicated, but really works well for convenience in the field or at the bench. The mix is simple but works very well in my guns for me.
When I'm lubing-up the next batch, I just drop the newly cast bullets into the holes in the pan where the last bullets came from and put the pan in the oven until it melts again.
My lube-pan is just a cheap 'brownie-pan' that isn't used for anything else.
Skillet