.30-30, .44mag, and shot gun might cut it back East, but out West those rounds are underpowered for larger game and longer distances. Early mountain men found this out and traded their small caliber eastern rifles for big ol' .50, .54, and .56 caliber rounds.
You could use a .45-70 at shorter ranges (I do), but for an all-around gun you need something with decent energy out at 200-300 yards.
Even a .45-70 loses a fair amount of energy after 200 yards and has a trajectory like an Irish rainbow. If you plan on choosing a .45-70, you better be willing to put in some serious practice time. Them rounds ain't cheap either.
Any gun is better than no gun, but in this scenario you need to put some thought into your choice. Consider the energy ratings (in Ft-Lbs) for some Federal ammunition at 200 yards:
.270 = 1992
7mm Mag = 2321
.30-30 = 947
.30-06 = 2026
.300 Win-Mag = 2411
.338 Win-Mag = 2729
.44 Mag = 672
.45-70 Gov’t = 1305
A general rule in Elk hunting is to be able to deliver 2000 Ft-Lbs of energy at bullet impact. Looking at the popular rounds above, which would you now choose?
Just my two-cents. I know there are guys on this board with more experience than I have, but this is how I think about it.