Fully automatic weapons have a short history, yet their inspection and methods of improving performance and accuracy of fire have been largely limited. Most of weapon performance parameters depend directly on the design of muzzle brake. The object of this work is to provide automatic small arms with a muzzle brake of a suitable design that would reduce its recoil velocity. This will reflect on the enhancement of the weapon performance. A number of muzzle brakes of different configurations have been manufactured and tested. The target was to predict the muzzle brake efficiency, and the fire accuracy. The test device permits the evaluation of the recoil of small calibre rifle by measuring the maximum number of recoil parameters at the same time. Measurements included the time variation of recoil force and accelerations for mechanical vibrations (horizontal and vertical) for an automatic rifle 7.62 x 39-mm, without and with muzzle brake. Furthermore, the projectile muzzle velocities, accuracy of fire and dispersion have been measured. It was found experimentally that the recoil velocity of the rifle could be reduced by about 35 %. Improvement of dispersion and accuracy of fire could be reached through the suitable design for muzzle brake. This work may contribute to solving problems in design and selection of muzzle brake geometry in automatic small arms with different calibres to enhance the weapon performance.