Confirmed by the included Colt factory letter this revolver is an experimental prototype and test revolver kept by the Colt factory. The letter also confirms the caliber, barrel length, blue finish with frame in the white, and absent grips. The left side of the barrel is marked "POLICE POSITIVE SPECIAL / .38 SPECIAL CTG." and the one-line Hartford address on top of the barrel. Comes with two attached tags providing factory details as presented in factory letter. One tag indicates "straight contour side plate", "Mod. D-.38 Sp." and "Fire 1000 rounds", with total rounds fired on various 1949 dates to 1002 and annotation "5-12-50 Reduced section @ Latch Pin & Thickness of Hand Increased". The other tag has the serial number and "Modified D Revolver / Square side plate / New Ratchet" and illegible reference to latch pin with further notation "Keep 11-23-51". The other side of the second tag has a monogram of a factory engineer (appears to be "HR"), "square side plate" and "over". Two small parts are tied to a tag.