In 1913 John D. Pedersen began working on a new autoloading pocket pistol. He filed for a basic patent on this pistol on July 30, 1915, but the war in Europe would soon put a halt to his efforts.
He revised his application after the war on July 17, 1919, and he was eventually issued a U.S. patent on August 3, 1920, although the pistol was in full production at Remington's Ilion plant at that time.
In all Pedersen and other Remington designers such as Crawford C. Loomis, G. H. Garrison, H. Askler, and C. B. Dygert were issued twenty-nine U.S. patents for improvements on the Remington Model 51 pistol over a ten-year period.
When developmental work by Pedersen resumed in 1919, Remington tooled up to manufacture this autoloader for the civilian market. After months spent changing over military production machinery, the first Model 51 pistols were ready in September 1919, selling for $36.30 each.
This hammerless pistol had the distinction of being the first new firearm developed and sold by Rem-UMC after the war. The action is a unique combination blowback-recoil system—a hesitation or impinging action. Initially these seven-shot autoloaders were chambered for the .380 Remington Autoloading cartridge, and full production was in effect by 1920.
Remington introduced a .32 ACP version of the Model 51 pistol in August 1921, with an initial selling price of $25. The magazine held eight rounds, one more than the .380 pistol magazine.
Remington announced on August 18, 1926, that it was discontinuing the Model 51 autoloading pistol. In all 64,796 pistols had been made in only seven years of production. Other than the venerable Remington Over/Under Derringer, the Model 51 would be the last pistol manufactured by Remington until the bolt-action, synthetic-stocked Model XP-100 was announced in 1962.