Whats the recoil like on the 50-95 with a 300 grain cast bullet?

Pretty light. You’re talking a huge rifle here. Mine is very comfortable to shoot.

I can't answer that, not having fired one.
But I do wonder where you might get new brass to load .50-95 in these times of shortages.
Or what you might form it from.

In any case I thought that you and the members might enjoy this excellent article, complete with great pictures and lots of information.

https://www.blackpowdercartridge.com/new-loads-for-the-50-95-winchester

Ammunition artifacts has brass. Nice stuff too.