A firearm apparatus and a method of firing ammunition therefrom, where the method utilizes a barrel (12) having a breech end surface (40) and immovably affixed to frame (10), a stand pressure surface (32), and a cartridge container (16) with a cartridge case (26) therein and countermass main body (18) movable in opposite directions. Gas from a deflagrating propellant moves the movable members and applies directionally opposite forces upon the breech end surface (40) and the stand pressure surface (32), which results in the force cancellation and ensures that the barrel (12) remains stable during firing. This solves the problem of the angle of departure and contributes to a high accuracy of shooting.