Colt model 1900
Colt model 1900 automatic pistol. Caliber 38 rimless. Manufactured between 1900 and 1903. About 3500 produced. Most of the production has the slide altered. The original safety was not that safe and was altered to prevent the slide kicking of the gun when fired.
Exists with front and back serrations. The front serrations are pretty rare.
The model 1900 was colt's first production in the category of the automatic pistols. Some US army marked models exist but are pretty rare.
Photos Littlegun