This compensator fits the HK USP 45 full size 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), to the match barrel length (which achieves the least recoil reduction). The compensator is made of steel and has cooling vents to help keep the temperature down and adds about 12 ounces of weight to the firearm.