The rifle was based on the Mauser Gewehr 98, with the action modified to sustain the higher pressure and length of the new cartridge and the barrel lengthened significantly. The first tests carried out in Brześć and Pionki showed that the new weapon was capable of penetrating a 15 mm steel plate at a distance of 300 metres with similar results against angled steel plate. Initially the barrel could withstand only about 30 shots, after which it had to be replaced with a new one. However, this drawback was soon corrected and the final prototype could fire approximately 300 shots. The committee accepted the new design on November 25, 1935, and in December the Ministry of Military Affairs ordered the delivery of 5 rifles, 5000 cartridges and a set of spare barrels for further tests.