MPX

The SIG-Sauer MPX is a Submachine Gun produced by SIG-Sauer. First announced in 2013, the weapon is available in several selective fire configurations for military and police use. The SIG MPX is a modular weapon which can be user-configured to fire three calibers: 9x19 mm Luger/Parabellum, .357 SIG or, .40 S&W,. It is a gas operated weapon, utilizing short-stroke gas piston and rotary bolt locking. SIG-Sauer MPX fires from closed bolt for enhanced accuracy and safety, taking ammunition proprietary box magazines, made of translucent polymer and holding 10, 20 or 30 rounds.

Battlefield 4
The SIG MPX is a weapon set to be introduced in the Battlefield 4: Dragon's Teeth expansion. It was first discovered in the the game files after a patch was released on PC.