Lots of cartrages including the 45/70 and 300 Mag could most likely harvest Deer and black bears along with many other furry critters.
Some of todays younger generation under estimates the potential of what worked well many years ago.
The old school 45/70 can reach out there far past the little 400 yard mark easy.
Loaded with the 500gr lead wad it will plant the lead ruffly 12" deep into the ground at the 1500 ish hundred yard mark.
One would think that any small Deer or small black bear would not like being tagged by one of those heavy weight wads.
There a fellow on YouTube running the 45/70 sharps off simple X sticks tagging iron silhouette at 990 yards with the old flip up rear sight. In the winds.
https://youtu.be/st4qE02GEKo
Yes, this can be done with the 300 Mag and many other cartrages too.
On the real side of this is the normal game Harvesting one would be with in the under 400 yard mark.
This is still not out of range for either rifle.
Lots of folks talk about hold over, flat shooting, and bullet drop... I'm guessing that all projectiles have some kind of drop.
This is taken care of with sight adjustment. The old sharps sight is pretty fast.
The Open peep hole sight allows for clear magic ring eye adjustment from 25 too 200 yards with the right open game aperture disk in place. This is done by eye,,, the other options are hold over or bump stop the sight too the range the critter is.
Most sharps peep ramp sights come factory with 1000 yard adjustments.
Long rails are available depending on what grain of lead one wants too put down range.
The old school rifles are coming back in the USA since folks can cast their own bullets, and a person feels pretty proud of them selves when taking a critter or pounding away at iron silhouettes from 200 too 1000 yards with their own unique hand loads.
Again, the same can be said about many other cartrages too.
What really counts over and above all is that the person them self is the one who gets to pick and choose what works for her or him.
Its all win win as each persons finds the path that best suits their needs.
Don from Western Canada