Lyman #48 shows 45.5 grains of 3031 as start and 48.0 grains as max for their Trapdoor data. These yeild velocities of 1580 and 1661 respectively. Lymans' Lever Action data shows 48.0 grains to start, 51 grains max. Velocities are 1657 and 1881 respectively. This last load, 51 grains of 3031 is a duplicate of teh factory Winchester 300 grain velocity, but probably operates at a little higher pressure, 25,300 cup. You may want to go and visit the IMR website, you can download their data there.
IMR 3031, Reloder 7, and IMR 4198 are all three exellent powders in the 45-70. There is a good bit of data available for using pistol powders from Unique to 2400 driving 350-400 grain bullets to velocities of about 1200 fps for good plinking loads as well. Stay within lever action loading data in your NEF. It will probably take Ruger level loads, but there is little reason to go there as 45-70's with 405 grain bullets at 1350 fps have killed everything on this continent as well as a few others. One cannot drive the 45-70 fast enough to flatten the trajectory enough to matter. All that can be done is adding energy to the bullet, which will not nessicarily make it a better or cleaner killer. The factory 300 grain loads at 1800 fps have a remarkable reputation for being outstanding killers. Of the 45-70 I will say this, on whitetails hits are obvious and unmistakeable. Good Shooting, JP
