Don't get me wrong.
The Marlins and other carbines etc are wonderful rifles, but were not designed to be used with the barn burner cartridges that are coming out today..
That is not to say that they can't handle them by any means..
When the Marlin and Winchester saddle guns were developed it was for black powder loads etc..
They were comfortable to shoot and dammed fine guns, but the were not ergonomically designed to absorb the recoil of the modern cartridges of today.
I think a model 94 Winchester 30-30 is one of the hardest kicking( for the cartridge) rifles there is around.
Somebody mentioned the Cavalry troopers and the need to reduce the bullet weight and powder charges in the carbine rounds. There is a lot of truth in that info.. A 45-70-500 will knock the snot out of you in a cavarly carbine.
The Marlin and Winchesters etc are even lighter than the old Trapdoor Carbine..
If you want to have an enjoyable time with a 45-70.. Load it to the velocity and with the bullet weights it was designed for.. Learn to shoot it using those criteria and you will enjoy shooting it and gain a great respect for the guns and the old timers who used them.
I have taken antelope,coyotes,deer and elk with the ol 45-70 Gummint, I have hit a full size metal buffalo at a 1000 yrds, but not with a carbine..*G*.
I am not demeaning the new uses for the 45-70's for hunting etc by any stretch of the imagination.. I may get one of the new Marlins myself.. I love the 45-70 cartridge and I would guess I have sent a ton of lead down range in 500 grn increments.
I am just suggesting you try the original loads and find out how much fun a 45-70 really is.. Not how bad it hurts..
You can put a Ferrari engine in a Model T and it will probably go 150 mph, but you ain't gonna enjoy the ride!!!