I am somewhat puzzled as to why the 45-70 has to be hotrodded. The 300 grain bullets of just about ay flavor work great for fairly big critters at the 1800fps. I have had my perceptions altered by using my old Sharps. As a rsult, I am working in 2 cast bullet loadings that use a relatively soft cast (20:1) bullet at a relatively mellow (1400fps) vel. The Marlin appears to like both and using an old style barrel sight (ladder), the range settings are quite accurate. MUCH easier on my rifle, brass,shoulder and powder supplies while giving performance that is near what my old buffler gun gives. I don't think these things will bounce off of much. Match a rifle sight like mine to the loading you use and it can and will kill BIG critters farther away than you might believe.
The reason I try to run mine at 2200 fps is that I use a .30-30 quite a bit, and I am attempting to emulate it's trajectory. I've been using the .30-30 for a long enough time that the trajectory is second nature to me, and duplicating it seemed like a good idea (one less set of figures to remember).
Recoil is just a bit different, though.
If I were hunting larger game, I do have a couple of loads that run a 430 grain LBT style gascheck at 1650 and 1800 fps, and they will shoot through just about anything I want to hunt with that rifle.
