Aim\ Some questions about the mechanical firing of the firing mechanism in large caliber rotating barrels machinegun are discussed. Methods\ The characteristics of the firing mechanism in rotating barrels machinegun are studied and some simulation tests of this machine are done. Results\ How the rotating speed of barrel bolt receiver greater than \{300 r/min\} this machine must guarantee receiver is the most important. Conclusion\ These results may be useful when the firing mechanism in rotating barrels machinegun is designed.