Your gun appears to be a Facile Priceps action from c. 1891, originally UK proofed for black powder.
The 1839 refers to the Greener ejector system patented 1881. Don't know if the 2003 is a 'patent use number'or not.As previously posted it appears to have been rebarrelled in Ferlach, not sure of date etc, probably Nitro by then but I am not familiar with German marks. Your 28.5" barrels would equate to Continental 725mm and 685 at the muzzle would give you 40 thou full choke at 725'ish bore or a bit more if the bores were 729 .
I would guess the stock is also a Ferlach replacement, never seen a Monte Carlo stock on a Greener but he did produce some 'funny' styles.
Not sure of the original Greener grade, I am sure of the more knowledgeable here will know.
