There is German Silver and there is Nickel Silver. The terms are interchanged in common usage, but they are distinctly different.
They are similar, but German Silver, which was used on 19th century rifles, has a slight yellowish cast. It is very hard to find now. If you do find some, a good restorer would love to have it, in order to match the old inlays.
That is because the common, and newer, alloy now is called Nickel Silver. It has a little more nickel in it, which makes it more white. The good news is it is just a very little closer to real silver in appearance.
% alloying elements
Alloy name UNS Number Cu Zn Ni
Nickel silver, C75200 65 16 18
65-18
German Silver, C75700 65 23 12
65-12
The only reason to know the UNS number is when you are buying some from a distributor. That UNS number is the definite description of what you are getting. You might see the old Copper Development Association numbers used instead, e.g. C752 or C757
Depending upon Pocket Depth, real Sterling silver 92.5% silver 7.5% copper is always in good taste. Some old inlays would have been of coin silver, 90% silver 10% copper. It is slightly less white, but it is much simpler to find some coins & hammer them out than to buy sterling sheet.