1891 Argentine
1891 Argentine Cavalry and Engineer Mauser carbines in 7.65.
I think that would be the oldest firearm, though that model was produced for a few years. I do have a 1898 Krag with a 1902 stock cartouche on it. Shot deer with both the 1891s and the Krag. The 30-40 Krag doe was this month.
Once, I fired a perfect score on the Texas Concealed Handgun Qualification course with a Smith and Wesson .44 Russian revolver that was sold in a St Louis hardware store in 1874....two years before Custer got it at Little Big Horn. Not mine though. Dang fine pistol.
Shot a doe with 1903A3 from 1943, a K98 Mauser marked 1937, and a P17 from WWI as well this year. Got a 1937 Luger and a couple of old Colt 1903 pocket models that fire and function without problems. Got an M38 Swede that is an arsenal rebuilt 1900 Gustav. Shot a couple of does with it a year ago.