I also have an XD40 with an EFK 9mm conversion barrel. I've only just got the DGR and 22# spring and ran about 100 rounds of WWB 9mm through with the 22# and it worked just fine. I will reply again later when I experiment more with it. BTW the 9mm with the 22# spring made recoil and muzzle flip almost non-existant. Hell even my fiance` (with small hands) loved shooting it.