Madbull is one of the top manufacturers in the airsoft industry, they are world renowned for their high quality products and their tight bore precision inner barrels are no exception. The Madbull Version 2 Precision inner barrel features a 6.03mm diameter for increased range, accuracy, and in some cases increased muzzle velocity.
I have an A&K M60 VN. This barrel improved performance in all categories, and with .25g bbs, I was out-ranging and more accurate than any sniper I've faced. Definitely a worthwhile upgrade. Turned my beast into a mean killing machine.