There’s a .45-120, I’ve heard. Sounds unpleasant to shoot. I was out shooting some 300 meter one day and a guy turned up in the next bench with a Martini-Henry. I got to play with it. VERY fun shooter.
They made some .50-140’s too.Navy Arms used to chamber their rolling block replica in that caliber,among others.The empty brass were over 3 inches long,paper patched bullets were up to 700 grains.
Firing 20 rounds rapid fire should give you a work-out similar to a couple rounds with an MMA fighter.
From Zulu Dawn (1979)
Corporal Storey: [to the soldier next to him, referring to the ammunition] Soft ‘eaded buggers these. Flatten out against the bone. Smash ‘em out.
Storey’s mate: But bullets run out... and those bloody spears don’t.