Leroy Lettering Light  Suggested by donshottype 

Not a standard retail font.
Might have been stamped from custom lettering or milled on the steel.
The _R_ and _S_, and the less distinctive letters are a fair match for some of the standard faces used by the Leroy® Automatic Lettering Machine, which exist in several digital versions.
The closest overall to the lettering on the sidearm might be Character's Leroy Lettering Light, 2003

Not at Dafont, but is at Fontspace