Today, I´ve tested my new compensator for the X15. Karl Hamann (-> www.waffentechnik-hamann.de) modified a Bennie Cooley compensator that I could clamp it on the barrel of the XR15. So no modifications need to be made on the XR, just clamp it and you are done! The comp works very well. The recoil and the muzzle flip are very reduced!
Here´s a short movie sequence of the comp (see the gas flow from the comp):