I just picked up a Shikari 45/70 in dang near unused condition and understand that these old boys are laid back and can't take the high strung loads. However, I've read three different pressures for 'em at 18k cup, 21k cup, and 28k cup as a max load. I have a loading in mind from doubletap ammo that lists the following load.
A 45-70 load that will deliver superior penetration on big game and remain safe to shoot through all guns chambered in 45-70 (except the old trap-door style). This load runs at 25,000psi yet has the ballistics found in much higher pressure cartridges. Deer, elk, moose, hogs, and bear will not like this one!
Caliber : .45-70 Government
Bullet : 400gr Wide Flat Nose Gas Check
Ballistics : 1810fps - 2914 ft./lbs. - 22.0" bbl. Marlin
If the max is 28k cup as some believe this would be a safe load, however d.t. doesn't believe so. I don't reload so I'm having a hard time finding ammo that's hard cast. I've found some winchester supreme with the nosler 405s that are at 1400 that look good but I would really like to have a hard cast round for Utah elk.