Great to hear from you.
I have two Powell .500 3" BPE rifles and an H&H .500 3 1/4" BPE rifle.
I use 450 grain Barnes Originals with Pyrodex in all three. The bullets can
be purchased directly from Barnes. As I'm sure you know, original loads used
a 380 grain paper patched bullet with a copper tube. Later nitro-for-black
used a 440 grain bullet.
My load for the Powell's is 85-90 grains of Pyrodex with the 450 Barnes. Can't
recall if you know Mal Weaver but the same load regulated in his Dougall and he
nailed an elk with it.
If you need more details use firstname.lastname@example.org