This compensator fits the HK USP 45 Compact of all barrel lengths. The compensator has a fully open top to accommodate all barrel lengths, due to the fact that the barrel pitches when it is fired. From the standard full size (which achieves the most recoil reduction), to the tactical barrel (which achieves slightly less recoil reduction). The compensator is made of mat black anodized aluminum and has cooling vents to help keep the temperature down and adds about 4 ounces of weight to the firearm.