Hunting With Cowboy Loads?

[Mr. 16 gauge]

I guess a lot depends on caliber, bullet style (SWC vs RN), type of weapon, range it will be used, conditions it will be used, how accurate you are with your chosen weapon, ect.

If it was a big (.44 or .45 cal) bullet with a big meplat, and ranges were short and the deer are on the smaller size, I wouldn't have a problem with it.
On the other hand, I feel that it is the duty of every hunter to use the best ammo/cartridge combo possible to make a clean kill, so if a modern version of the same cartridge is 'better', i.e. more velocity, ect, then I would suggest going with that.

FWIW..