Hi, Vt.birdhunter,
Nope. An American gun writer, for reasons unknown, described the Sarajevo gun as a 1900 Browning; that was not true. The actual gun was as I described; it was in a Vienna museum, along with the other three guns and the grenades carried by the attackers, but which were not used. The display vanished during the Russian occupation after WWII, but the Princip gun has since been recovered from, of all places, a monastery.
FWIW, I think only the Sarajevo gun and the I.J. revolver used to kill RFK really fit the OP's definition. The guns used in attempted assassinations don't count because they changed nothing. Other guns, like Patton's, might be interesting but altered nothing so far as history is concerned.
Jim