Hey Crash,
I think it is a font supplied by (or sold by) an engraving machine maker by the name of Gravograph. It looks like it might be be either "US BLOCK 1L" or one of their "SL" series of fonts (SL meaning "single line" as far as I can tell). It would make sense that you (or I for that matter) are having troubles finding a common font that matches as Gravograph would have altered a font to suit their machine and software. I believe engraving fonts need to have specific tool paths written and it makes sense to design fonts that are clear and with the least amount of motion or lifting. Also, it makes sense it would be an engraving font that would match your guns markings. Only thing not making sense to me is the font seems to match their logo? Anyway, just google "US BLOCK 1L font" and follow the few links that are there. Good luck....