An improved compressed gas operated pistol is provided which maximizes use of compressed gas energy by minimizing loss of energy from the chamber into the magazine. An aft end portion of the barrel of the pistol is formed extended as a thin wall portion. When the trigger of the pistol is actuated, this thin wall portion of the barrel is fitted tightly into the chamber, confining the next pellet to be fired within the cylindrical walls of the thin wall portion and the rear surface of the chamber, and sealing off the chamber from the magazine. In this manner, the full impact of the energy provided for firing by the compressed gas cylinder to the chamber is imparted on the pellet.