This is a full auto Thompson 27A1 converted via registered Broadhead Armory full auto firing pin (Model: M1927, SN: BA-GG003, on ATF form 4). It is built on a custom 27A1 semi auto receiver with Colt 1928 Navy model markings, but has the dimensions of a Thompson 27A1. Note the serial number on the receiver (15041). This number is one digit higher than the serial number of the last Colt Thompson made in the 1920's.
Photo and information from: Michael Sennett