I had identical keyholing with my .44 mag Browning B-92 with .430 Missouri bullets. I solved my problems with .432 bullets from Penn bullets. Sadly, Robert Palermo, owner of Penn bullets passed away last year and his wife is not carrying on with the business.robertb wrote:. . . Unfortunately, they are keyholing at 50 yards which tells me I need to go up in bullet diameter. . . . what diameter bullet is working for your 92 .44 mag?
I have a pretty good personal supply but have not found another source for .432 bullets -- but I haven't looked hard. FWIW, I'm pleased with bullets in other calibers from MBC. I use their oversize (.311 instead of .308) bullets in my Marlin 336 30/30. I'll check to see if they'll considering doing the same for those of us with rifles with the SAAMI .44 mag specs.
Or, you could cast and size your own . . .