How are you measuring your throats? If you can shoot .452 lead bullets at ANY velocity/brinell rating with no leading I have to think your throats are not as big as you think?

Mine (.458) is a leaded up mess no matter what lead/powder combination with .452 bullets. After only one round you can see the leading. It only makes sense that the hot gases are blowing by the bullet in the throat. I tried fast/slow powders, fast/slow velocities. No combination would obturate a .452 lead bullet.

.451 jacketed bullets avoid the leading but accuracy is even worse. (In Ransom Rest)

I missed out on a like new .453 cylinder on GB the other day for about $80. Da**