The 300 grain HP bullets expand well in the 45-70. The Heavier round nose like the 350 Grain Hornady Interlock need top 45-70 velocities to expand in Game like bears. Reloadig is what gives a hunter a wide range of versitility as most all calibers have bullets available which perform well on thin skinned and also heavier game. Also at a wide range of velocities. Sectional density also has a huge effect on bullet expansion low SD bullets will expand in small game and varmits but will probably blow up on heavier game. High Density bullets may well punch small holes through lighter game and have no or very little expansion. Sd of 200-250 is about right for deer while 260-300 is suited for elk and 300 on up for very heavy beasts with thick hides. This changes a bit with heavy pistol bullet with less density but wide flat noses.