I have not shot a Marlin Guide Gun but have shot my 1886 with steel carbine butt plate. It weighs ~7 lbs. My .338 weighs ~9 lbs with scope. I don't care to shoot the 45-70 even with light loads from the bench but can shoot the .338 quite a bit. I do have a pre 64 .300 H&H with steel butt plate and would rather shoot that than the 45-70. Once I put a Simms slip-on recoil pad on the 45-70, I can shoot 400g bullets at 2000 fps fairly comfortably. It still seems to move me around more than the .338 however due to the shape of the stock.
