No one is advocating to do anything unsafe. But there's target shooting and combat shooting. Folks want to maximize their fun factor with their gun. They want to enjoy the boom and the roar of their gun. Doing that is not quite the same as trying to turn the gun into a magnum and not being able to hit anything with it. .41 mag. or .44 mag. cartridges cost well over 50 cents per round, and even if shooting those rounds the guns aren't always controllable or enjoyable to fire. Yet, for the cost of a few cents more of powder and adding some compression to their cap & ball loading method, folks can charge their 1858's with 40 grains of powder and fire what they consider to be a satisfying, enjoyable boom that produces at least some kind of combat accuracy for a fraction of the cost.
Shooting 40 grains of powder in a .45 rifle with a .440 patched round ball is a target load and a weak one at that.
Now all of a sudden loading 40 grains of powder into an 1858 is chararcterized as trying to turn it into a .44 magnum. Hardly!
Folks have complained that the cap & ball guns are too weak and anemic to be effective for self-defense. But they do have the capability of being loaded up for the purpose of having a better one shot stop capability.
Then there are also close hunting purposes like from a tree stand.
And there's the Buffalo model with the 12 inch barrel that can produce some extra accuracy and velocity from the longer barrel.
And there's modifications that can be made to their barrel throat and chambers that can improve accuracy and performance even with some of the more potent loads.
So 1858's aren't only about target shooting.
There's a fun factor that appeals to some folks.
There's extra room in the chamber for loading conicals or for adding a little bit of extra powder. That's not the same as loading an inline with 150 grains of powder. After all, shooting 40 grains of powder in a .45 rifle may not even be considered to be a point blank deer load.
So let's not try to compare doing that to shooting the magnums.
And if black powder is more controllable and enjoyable to shoot compared to the more expensive rounds, then let folks have their combat shooting experience in a safe and enjoyable way.
If they're unhappy with the performance then they won't do it, or won't do it much.
Or they will consider moving up to a Ruger Old Army, or a Colt Dragoon or Walker.
Or they will use another powder that produces more power without using too much extra powder like 777, Swiss or Pyrodex P.
It's only about having fun and being able to blast away safely and economically.
If some folks don't want to blast away then they can be totally happy buying a brass frame gun and shooting the recommended 25 grain loads. But if folks have invested in a steel frame Remington and want to experience the heavier loads, then it's safe to do within its range limitations. And if they're not happy with the performance then they won't do it. So then let's not generalize that 1858's can't be effectively used for the purpose of self-defense and combat style shooting, especially at closer combat range like across a room or two.
Even if folks want to fire a 2 inch barrel gun that's loaded up with a stout powder charge then more power to them. Everyone should enjoy themselves and their choice of a safe shooting style.