I was using a 6” barrel; finding a long-barreled 50 AE is nearly impossible. However, .45-70 is readily available in longer barrels - it’s a rifle cartridge, not a pistol cartridge. And you can find .45-70 ammo all over - is 50 AE easy to find?
I worked half a dozen summers as a guide in Alaska (outside of Dillingham, up in the 5 lakes area), and about the only thing any serious guide would consider is either a .45-70 or a 12GA with slugs. Most .45-70s were Marlin 1895s with a barrel cut down to 18” (just a little longer than the magazine). Also make a handy club if needed!
A few liked 458s and 30-06s and some used 338s (mainly way up North in polar bear country, where longer shots might be needed), but it was shoulder-fired weapons to a man, and usually levers or pumps (nice and reliable and easy to operate, even with a bum arm). Semi-autos were never seen - not enough trust they’d always go bang multiple times, and it’s hard to clean the action if it falls in sand, dirt, or - as I’ve seen once - filled with ice.
Some guys carried pistols as well (I carried a Glock G20 - capable for anything smaller than a bear or large buck), but those were backup or for smaller predators. For the grizzlies - or even scarier, bull moose in mating season - it was the .45-70 that protected you.
For grizzlies, the general consensus was too big is almost big enough - you just don’t want to risk anything smaller or less accurate. You get maybe 2-3 shots off on a charging grizzly before they’re on you - every shot MUST count, and the must have enough punch to go through the front of the bear deep into the heart and CNS area.
Personally, I’ll take the .45-70 every time - it’s proven in the field for grizzly and even polar bear work. If you’re comfortable with the 50AE, go for it, but I never saw it out in the field, and have a hard time believing any pistol cartridge will provide equivalent energy to a strong rifle cartridge, and I personally prefer the stability and accuracy I get with a rifle as compared to a pistol - especially a strong recoiling pistol.
.50AE ammo is much easier to find than a suitable gun to fire it in.
There may be some .50AE pump-gun conversions on the market fairly soon. ;-)
Our local bears around are are just blacks, .50AE drops them with ease, one shot.