principle of compressed gas expanding to force a pellet down the gun's barrel and each type has its own advantages and disadvantages. A Tokyo Marui M14 , Marui MP5 A4, G&P M4 - CQBR , Jing Gong XM177E2 , Galaxy MP5K-PDW , Maruzen M870 BV, Tokyo Marui P226 , KSC M92