It was repeatedly said you could shoot .458 Win. Mag. from the Watts. What wasn't told was the guilding material fouling in the chamber. 1 or two shots might not make any difference, but quite likely 10 or 20 certainly would.
Jack fixed that with his change to the chamber design.
The same thing would happen in a .45/90 M86 (or any other (.45/90) if .45/70's were shot in the chamber. It was slightly more likely, the greater the difference in chamber lengths, such as shooting a .45/70 or .45/90 in a 3 1/4" chamber.
I'm surprised Phil Shoemaker hasn't addressed this thread. He used a .458 M70 for many years as a backup for his grizzly/brown bear hunts. IIRC he liked the 400 grain Barnes X bullet for that purpose at about 2,300fps.