Shooting a while back the tube blew off leaving the nut and screw holding it still attached to the barrel. I ordered a new nut and screw thinking these were defective. The tube appeared to have no damage. However now the tube simply slips off over the screw which is tight. The tube, although flush against the barrel will not hold. I can't understand what is supposed to hold it there in the first place, tension? Logically a screw with a head would pin it on nicely. Is my tube damaged after all? Any help or ideas welcome.