Cap'n Redneck, thanks for your response. I use a compression die to compact the powder down to the proper depth so when the bullet is seated and crimped with a Lee factory Crimp Die the cartridge OAL is same size as the 500 grn bullet at 2.76 and it does fit nicely into the chamber of my trapdoor. Both the Chey-Cast and the Buffalo Arms bullets are soft cast 20-1 alloy. I made up one round yesterday to set my dies up for this different round and to attain the correct overall length all on top of the 70 grns of BP but I just wanted to pick some brains out there that may have a wider background and experience in loading for this old trapdoor to make sure that using a bullet with the extra 12 grns, which is additional length of the round, would not be problematic. Tomorrow I will load up the rest of the 50 rounds and take it out to the range soon.
Thanks,
Tater Pickens