Remington 51 Prototype

The 380 CAL designation was not thought to have been used until .32 production began in 1921.
This is the only prototype to have the caliber designation on the barrel--even the .32 prototypes do not have it.  Yet this barrel has two notches, and the breech block has the cartridge guide lug. There is another late prototype, S/N 545, in the Wells Fargo Museum, that has all the characteristics of this gun, except it does not have the .380 CAL designation on the barrel.