Howdy Pard:
I have shot 45-70's in every conceivable type since my first Springfield with black powder when I was 14. That's 40 years. I have also shot every load you can imagine on deer, moose, bear, even grouse, as well as long range sillhoete. My opinion after all this smoke is that the best all-round load is 400 gr. lead with black powder or its smokeless equivalent. Those 300 hollow points are going to ruin a lot of meat unless you put it through the ribs just right. I recently converted a friend to Marlin with factory 400's at 1300, and when He recently shot a large bear with it, it collapsed in its tracks, much to the amazement of the dog men with him. Use them 400's nice and slow and learn to hold over and dope the wind. Save your shoulder in the process.
Good luck.
Ps. Nice smokeless powder for this type of load is Sr 4759. But, black is the most fun.
