The style of the powder charge/bullet type mark is what was used between 1892 and 1912. After 1912 it became

St.m.G.
-------
13 gr.

That is, bullet type over bullet weight, no mention anymore of powder at all. It's also not usual to see just crown-over-N (nitro proof), there should also be crown-over-U (final inspection) and crown-over-G (rifled barrel).

Looks like a very nice "mom-'n-pop shop" German sporter, and it appears to shoot really well - congrats!