ST-57 is originally a PDW type upper receiver for M4 / M16 Lower receiver, which is designed for firing 5.7x28mm round from standard P90 Box magazine. User can buy the Receiver Kit only as they want to bulid up the rifle with their original lower receiver, or they can buy as a fully assembled, stand alone rifle in semi-auto. Full-auto version is now available but only marketed to Law Enforcement according to US Law.

Features :
Comes with One-piece CNC Made Upper Receiver with moveable cocking handle and Rail System Hand Guard Assembly.
Comes with a Metal Flash Hider in 14mm CW and a 10.5” barrel.
Comes with a PEQ type Battery box which can install 8.4V PEQ type Battery or 7.4V Lipo Battery (front-wire with small plug).
Comes with Flip-up Iron Sights.
Adjustable hopup system.
Comes with a M4 type lower receiver with M4 Magazine Catch which can clip a M4 AEG Magazine Shell for Ready-mag type battery or mini type battery.
Constructed of S&T Custom 8mm Ver 2 Metal Bearing Gear box.
Comes with Metal M231 Retratable Stock with 3 Positions Collapsible.
Ready to go for 400 – 420 FPS without modification.
Included a 57 rds P90 Mid-cap Magazine.
Compatible with Tokyo Marui / Tokyo Marui based P90 AEG Magazine.


Specifications :
Length : 665mm / 780mm (stock extended)
Inner Barrel Length : ~300mm
Shooting Mode : Safety, Semi, Full-Auto
Weight (Gram): 3540 (gun with magazine), 4740 (With Box)
Gearbox Type :  S&T Custom 8mm Ver 2 Metal Bearing Gear box
Color : Black
Power Source : 8.4V PEQ type Battery or 7.4V Lipo Battery (small plug)
Magazine Capacity : 57 rounds
Materials : Metal and plastic
Bullet Type : 6mm BB
Power (Muzzle Velocity) : 400 – 420 FPS
Manufacturer: S&T