The only real downside is ammo.
Factory ammo is quite expensive - 20 smokeless rounds for $85, or 20 black powder rounds for $90. (Ten-X)
Brass is hard to come by and expensive.
The upside to the brass problem is that it's relatively easy to make from .348 Winchester cases, but a bit time consuming. Cases can also be made from .50-70, .50-90, and .50 Alaskan, but .348's seem a bit less expensive and easier to come by.