LOADING CARTRIDGES FOR THE ORIGINAL .45-70 SPRINGFIELD RIFLE AND CARABINE. by J.S. and Pat Wolf. second edition by Pat Wolf.
The original .45-70 government rifleload (45-70-405) in 1873 was 70 grains of blackpowder with use of a 405 grain hollowbase lead bullet. And for the carabine (45-55-405) the original load was 55 grains of blackpowder also with use of a 405 grains lead bullet.
The 500 grains bullet came in service for use with the new and improved Buffington-sight in about 1884.
Large rifle Magnum primers are the best for use in the .45-70 cartridge.
all loads below 65 grain blackpowder are not needed to be pre-compressed but from 65 tru 70 grains of blackpowder you need to pre-compress the the powdercharge with a compressor die to provide room for the 405 grains HB bullet to seat.
If you try to compress the powder with the bullet there will be massive deforming of the bullet. The bullet and the powdercharge are best seperated by use of a card-wad.
Pre-compressing will cause better ignition and provides better burn of the powder with less bore fouling.
a heavy taper-crimp is required in a seperate and final operation for proper ignition of pre-compressed powdercharges. If the crimp is performed in the same operation as seating the bullet, the bullet will be damaged and accuracy will be affected.