I have had no better satisfaction out of any other weapon I have purchased than my Marlin 45-70 CB. It has become my weapon of choice on my Hog and White tail hunts. I now reload for it and with good results, as good as my eyes are with iron sights. I have chosen to keep the stock sights for now, but if I do change them, it won’t be to any type of scope, it will always have iron sights. I have plenty of scoped guns. I also have the guide version with the 18 ½” barrel but prefer the Cowboy version.
This is what I have found to work for my 1895CB 45-70.
Go with what is published by those who know
not by what I use, but it will give you some ideas. That's my disclamer.
For big game. I really like this one, because I like a good heavy kick.
Elmer Keith's classic load of 53 grains of IMR 3031 with the 405 grain bullet.
Or for smaller game:
From website
http://data.hodgdon.com/main_menu.asp300 GR. SIE HP IMR 4198 .458" 2.525" 54.0(min)-58.5(max)
The Elmer Keith’s load goes clean through Hogs and White tail, so the lighter HP may be a better choice for them. Both will do the job just fine.