Outer barrels have a notoriously sloppy fit with inner barrels, grossly reducing performance. Pair this with the EHSR and o-ring mod for an absolute zero wobble ROCK SOLID barrel for maximum performance. Simply drive this wedge between your inner and outer barrel at the muzzle, trim the excess, and replace your muzzle device. This is one of the few mods out there which you can really see huge improvement right away with very little work. This is an excellent companion product for the R-hop.