I have a 45-70 barrel from SSK since the 80's.[reg contender 14"] They can be loaded pretty heavy even in the old model contenders design. I remember asking JDJones how effective would it be on whitetail. His reply was that I would be able to see when the bullet connected. The first deer I shot was a doe approx. 135 lbs. The deer upon impact took 4 steps sideways and fell over. [He was not kidding] I was loading a 400 gr Speer at 1300 fps. Since those days I really don't feel the need to use anything heavier than the 300 gr jacketed bullets.