The 50AE pushes out around 1600 lb-ft at the muzzle, about half of a decent load for the .45-70. It's not even close in terms of energy.
If you HAVE to have a pistol, go with the S&W 500 - that has something closer to the lower end of a .45-70 - up around 2500 lb-ft of energy. But you still have the same problem as with the 50AE - trying to contain and CONTROL (you have seconds, after all, to get a few hits on target) that much power in your hands.
No thanks - give me a Marlin 1895 with the barrel cut down to 16.5", and 5 rounds of hot-loaded .45-70 with 420 grain hard-cast bullet at 2000 fps, for a solid 3700 lb-ft of energy with enough bullet weight and integrity to punch deep.
What length barrel are you citing?
I got 1900-2100 FPS out of a 16” barrel with 300 gr. bullets.
Having spoken to people who have actually used .50AE on bears, it works very well, much better than .44 mag. and miles ahead of .45 acp!
The Auto-mag V is reasonably light, unlike the Desert Eagle, recoil is still reasonable.
I’ve fired 500SW, do not want one, too punishing to the shooter.
I prefer a pistol as a rifle/shotgun can be awkward.