Butts were not something changed "in the wild".

As you noticed, the ferrule (socket) is tapered, as is the wooden bit that plugs into it. At the factory and in bigger workshops, they had a special press that drove the very-well linseed-oil-saturated butt into the body until the "tenon" was very hard up against the flat steel internal face of the ferrule. Then the stock bolt and washers were wound in until they squeaked. There IS supposed to be a small gap between the exterior rear of the receiver ferrule and the "wrist" of the butt, otherwise chunks will eventually start chipping off.

If your bore is as "toasted" as it looks, your only hope is "special brew" ammo or a new barrel.

And as Bindi said, use open-based bullets if you can find them. These rifles are NOT immortal.