The PDI 6.01mm 7-Inch Inner Barrel for TM Hi-Capa 5.1 is a must have upgrade for precision speed shooters, or anyone else that demands the utmost accuracy out of their pistol. This inner barrel has an internal diameter of 6.01mm, the tightest possible diameter you can have around the BB. Furthermore it is 7" long, almost 2 full inches longer than the stock barrel on the TM Hi Capa. The increased barrel length will not only give you better range and accuracy but it will also drastically increase your guns muzzle velocity. This barrel designed for use with compensator kits or barrel extensions. This is one of the best bang for buck upgrades that you can get for your gun and see an immediate performance increase.