Available for the first time in this length, exclusive release for Brownells. The revolutionary, patent pending Drive lock design, uses three independent wedges that interface with the angular grooves in our proprietary barrel nut. This system clamps the rail onto the steel barrel nut with extreme force and precision, while also driving the handguard rearward towards the upper receiver. The slightly larger ID of that extrusion gives us more real estate around the gas block, even more rigidity than the M76, and takes longer to heat. SOLGW is not discontinuing the M76. That will remain in full production. They are just adding the M89 to the lineup. Ballistic Advantage AR-15 b Mfg: Brownells