Abstract: A firearm in the form of a submachine gun which can fire in either a semiautomatic or full automatic mode. The firearm is provided with a front sear, a front trigger and a rear sear/trigger in a construction which allows the operator to instantly change between the semi and fully automatic mode without a selector switch, even while firing. Other features include capability for ambidextrous operation, the use of two magazines each located in a separate handgrip and an improved muzzle brake configuration. In addition, an improved ejector and magazine catch assembly are provided. The firearm of the present invention employs fewer moving parts so as to require no pins or screws for the trigger, sear, bolt guide or bolt stop.