M1928 SMG is the first type of the Thompson SMG widely used by US Navyand US Marine Corps from 1930s. It was the enhanced version of theM1921 which comes with a weight added actuator for slow down the cyclerate of fire. It was used by US army, FBI and law enforcement until1970s.
T-57is originally a PDW type upper receiver for M4 / M16 Lower receiver,which is designed for firing 5.7x28mm round from standard P90 Boxmagazine. User can buy the Receiver Kit only as they want to bulid upthe rifle with their original lower receiver, or they can buy as afully assembled, stand alone rifle in semi-auto. Full-auto version isnow available but only marketed to Law Enforcement according to US Law.Below M231 Stock Version : -Comes with a PEQ type Battery box which can install 8.4V PEQ typeBattery or 7.4V Lipo Battery http://airsoft.tiger111hk.com/p23435/S&T-Metal-ST-57-Assault-Rifle-AEG-M231-Stock-Version-%28Black%29/product_info.html