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.