I recently acquired this piece locally.  The chambering ended up being quite a mystery, but I now believe it is 11.55X40.4R, which is an old target cartridge, according to the 1904 DWM catalog.  The bore is in decent shape, with some erosion at the breach, but the bore gets better as you travel down it towards the muzzle.  The cartridge shoots a 340 grain .458" bullet from a Lee mould to about 1200 fps or so.  The triggers are excellent, and even unset the trigger is quite nice and light.  There are no markings on the gun, short of a serial number.  The action itself is a bit of a mystery as well.  It seems like a combination of 1866 Chassepot and Mauser 71.  It shoots well, and I expect to take it hunting this Fall.  The last pic shows the chamber cast next to one of my loaded Werder rounds.
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The cartridge it is sitting next to is only 35 mm long.  The chamber itself seems to measure close to 42 mm, but there is going to be some buffer area.  I've actually started trimming the cases a little shorter yet, to match the crimp groove on my chosen bullet when it is seated just behind the lands.  I may decide to custom design a slight bore-riding design, I'm not sure.

The one I had back when had a little longer action - it was in 9.3x82R (that's eightytwo!). Would have looked impressive in a bandolier.

I saw one somewhat similar a few years back in a shop downstate IN. The stock was similar, a bit rougher but salvageable.   I suspected it was a stalker in 8.15x46r.  Went back a few months later with a dummy round and it chambered well.  I'd have bought it at a reasonable price, but the young shop owner had hallucinations of grandeur as to its value.   He was that way about all his inventory and only lasted a year or so.

Hello ,very nice gun. It looks a bit like this one ; it's a german bolt action rifle built by J.J. Reeb , 17mm caliber, probably an elephant hunting rifle.

Simpson Ltd has one such as you have shown but the stock is cracked through the wrist. gave it some thought but passed as my woodworking skills leave a lot to be desired. If interested look under single shot rifles in the search function. Frank