Peacemaker (Colt revolver)

“The Peacemaker” was the name of an 1873 Colt revolver. It quickly became the most popular pistol in the west.
 
Although “Peacemaker” is a curious name, “Peacemaker” was also used as the name for other weapons before 1873.
 
 
Wikipedia: Colt Single Action Army
The Colt Single Action Army handgun, also known as the Colt Peacemaker or Single Action Army, is a single action revolver holding 6 rounds of ammunition. It was designed for the US cavalry by Colt’s Manufacturing Company and adopted in 1873, and it was perhaps the most prolific pistol in the wild west. 
   
(Oxford English Dictionary)
peacemaker, n.
A gun or (occas.) other weapon used or able to be used decisively to settle a dispute.
Originally used of duelling pistols; later used esp. of a model of Colt revolver in widespread use in the U.S. in the late 19th cent. (see quot. 1973).
1841 C. J. LEVER Charles O’Malley vii. 40 The small mahogany box, which contained his peace-makers. 1861 J. R. LOWELL Biglow Papers in Poems (1890) II. 226 A feller..Lep’ up an’ drawed his peacemaker, an’, ‘Dash it, Sir,’ suz he. 1880 (title) Dr. J. H. McLean’s Peace Makers. A description of the guns, &c., manufactured by McLean and Coloney. 1963 N. H. MILLER & J. W. SNELL Great Gunfighters of Kansas Cowtowns (1967) 291 He would occasionally purchase a second hand revolver, notch the butt and give it away as his authentic ‘peacemaker’. 1973 J. QUICK Dict. Weapons & Mil. Terms 109/2 Introduced in 1873, this model [sc. the Colt .45 Single Action Army revolver], with slight modifications in caliber, is also referred to as the ‘Frontier’ or the ‘Peacemaker’.
       
11 March 1852, New York Observer and Chronicle, pg. 88:
Therefore the Porter Rifle was put forth as a messenger of Peace—a peacemaker.
 
27 January 1853, New York Daily Times, pg. 6:
Now, we have COLT’s revolvers, and rifles, and field pieces, and large guns—peacemakers and STOCKTON; the clenched fist has become a man-of-war.
 
23 September 1854, Gleason’s Pictorial Drawing-Room Companion, “Tales of Revolvers,” pg. 179:
Anecdotes calculated to propitiate the Peace Society appear in California papers, mentioning that large parties of Indians beholding those irresistible peace-makers in the hands of a handful of gold carriers, have been seen to drop their greedy eyes and slink away.
 
24 September 1950, Los Angeles Times, pg. D7:
THE PEACEMAKER AND ITS RIVALS.
An Account of the Single Action Colt.
By John E. Parsons
Morrow: $4.
The Colt was not the first revolver, nor the first to use metallic cartridges; but it was the first among cartridge revolvers to be officially adopted by the U.S. Army. Its title of “peacemaker” is dual; as an Army weapon, it waged a fight for peace; and as an instrument of frontier justice, the Colt spoke for peace in Texas and other southwest territories, on the range and in towns. The Colt concern itself called the revolver by the title of “The Peacemaker,” in its announcement of the new Army 45, and the name clung to the gun.