Vintage Belgian single shot 410 black powder Mauser 1871 action

This shotgun was built commercially in Belgium on a surplus  Mauser 1871 action around year 1890.m, or possibly they purchased new actions to build these.

Appears to have been refinished in a matt black on barrel and action, but bolt is original finish. 
Please ask for photos I took on takedown. 
Bore is bright but has pits right after chamber. Accepts 410 2 1/2” shells the gun is NOT nitro proofed. The 1871 action is strong (I think 43 mauser was 90 grains powder vs 44 grains or so for 410, so probably the action is plenty strong for 410 nitro, but barrel is not proofed. A gunsmith could ream the chamber a bit longer to accept 2 3/4” shells, and could maybe proof it for you. The wall thickness is substantial so probably safe, I would not fire a nitro 44-40 but personally I would fire a cast load. I would fire nitro shot shells. For those unaware, .410 can usually accept 44-40. But here a modern smokeless round would exceed the original proof pressures. 
I avoid bargaining but lower prices with time.