I have two here,
First is a .442 Webley "British Bulldog" used by one Charles Guiteau to assassinate President Andrew Garfield.
Mr. Guiteau was a Republican party member who had canvassed support for Garfield during the 1880 election, and expected to be rewarded with a government position (as was the fashion in politics at the time).
Guiteau wanted to be named Ambassador to the Qing court in China, despite not actually speaking Chinese and knowing next to nothing about China. Garfield, who had no idea who Guiteau even was, rejected his demand for a job.
So, after purchasing the aforementioned Webley (with Ivory grips as it would "look more striking in a museum)
So, after following Garfield's schedule for days (and neglecting to kill him at one point because Garfield had his wife with him and Guiteau "Did not want to upset the poor woman") He eventually struck on July 2nd, 1881, firing two shots that hit Garfield in the back, one shattering a vertebrae but not actually hitting the spine.
Garfield lingered for months before finally succumbing to infection (because his retarded doctors kept poking his would with their bare fingers.) dying on September 19th of that same year.
Guiteau was found guilty and sentenced to hang on June 30th, 1882. His last words was him reciting a poem he had written called "I am going to the Lordy", though famously, he was overpowered by the jeers from the crowd to the point he stopped and shouted at them, "You are all low, consummate jackasses!"
And that was the execution of the 20th president of the United States.