10mm is the new 45-70! It is rumored the physics was solved by Oppenheimer in his spare time after inventing the atomic bomb so this explains the mystery.
Seriously though, a 45-70 does not need to expand much, a 45 caliber bullet is already larger in diameter than an expanded .270 or .308. Kind of old the 1911 45 Auto vs 9mm argument, they make big holes going in and a .45-70 430 grain with a huge metplate makes a very large wound channel crushing bone and destroying tissue over the five to six feet of penetration it is capable of.
When I got my GG I tried a box of the Remington 405 grain jacketed (safe for all rifles) and it shot well with a solid push recoil, not bad. I tried a box of the Hornady 350 grain FTX and while accurate, the recoil was definitely more of a snap and noticeably more vigorous. The HMS Cowboy 405 grain is mild, more of a long push into the shoulder with authentic smoke, HMS Bear Load, is still a push, just a hard push. The BB is back to a snap, a very energetic and solid snap. My boss and I had been shooting and I pulled out the .45-70 with my 850 FPS reloads and was plinking away, shot a few Cowboy loads too and I loaded the magazine tube full of BB 430 grain HC. I warned him these were going to come back! He is a big guy, easy 350 pounds, he shook like a bowl of jello when that Marlin roared and he went back a full step. Those +P loads mean business.
I had originally set a Nikon African on Warne QR mounts and loved the 1X for rapid both eyes open shooting. Until it knocked my glasses off and broke them (safety rated eye glasses). The Marlin (and the Henry as well), while not lightweight rifles, are still around 8 pounds, most rifles with this level of recoil are a bit more weight. A 45-70 will come back at a fellow if you do not set the rifle solid into the shoulder with BB +P. I use a Burris Scout scope now. I want a .375 Ruger Alaskan with controlled feed, I will put the African on that pussy cat!