AR-15 5.56 NATO J&T Carlson Adjustable Comp 1/2x28. The “Carlson Adjustable Comp” is the first and only adjustable comp on the market today specifically developed for the AR 15 rifle. Select from three different gas port openings that allow you to choose how much gas is directed upward. This device can be adjusted to your rifle to allow for variations in factory and hand loaded ammunition. Give your AR 15 that custom feel with the Adjustable Comp.