of thrusting shoulders which meter and deflect the propelling gas the diverter cone 14 tapers from the diameter of the second cylindrical section 15 to the diameter of the cylindrical section 18 the diameter of cylindrical section 18 remains slightly greater than that of the bore 8 fig2 illustrates a third embodiment designed to maximize deflection of propelling gas which contains at least one additional gas slip 21 gas slip 21 is cut into the second cylindrical section 15 and is followed by an additional thrusting shoulder 23 to form yet another annular deflecting surface it is anticipated that the present invention would be machined into the muzzle end of barrel 2 using conventional techniques the ultimate goal of the invention is deflection of propelling gases by the progression of shoulder sections the initial gas slip is used to reach a maximum diameter for the first shoulder section multiple shoulders can then progress in a stepwise fashion through smaller diameters should additional shoulders be necessary the working diameter of chamber 22 is increased by an additional truncated cone such as gas slip 21 and the progression continues to the muzzle 19 thus an infinite variety of slip shoulder combinations are possible an alternative embodiment may be effected by the use of sections that are essentially in the shape of a cylinders of the largest diameter of each gas slip in place of the gas slip 12 a cylinder would similarily allow for the expansion of propelling gases fig5 is a cross section of the invention normal.