$$$$$ my friend, $$$$$. I am on a fixed disability pension so I must make or cobble together most of what I shoot.
: A .500 BPE would be absolutely delightful. My Engish gun collector friend has one that shoots into a 3" circle at 100meters, 2 lefts, 2 rights, with each bore's groups just over an inch. IT is pretty much perfect. The group centres are horizontal as well. It likes the hard #515141 Lyman bullet, lubricated disk wad and a case full of Pyrodex.
: His other BPE's about 8 of them, are all .577 and larger & kick too much for this old guy - but are fun to shoot.
: He's presently looking for a good 875gr. grooved bullet for the .577. I expect he'll get something from NEI.