Only time will tell, I've not had any shoot loose yet, but I haven't shot all that much thru most of them, the first barrel that I did the JB shim on is a 270 Win barrel, it has about 120 rounds thru it, still fits perfect, I've shot about 160 rounds thru the 500S&W with some pretty hot loads, if any were going to shoot loose, it would be one to put to the test. The compressive strength of JB Weld is 10.7kpsi, so it should hold up plenty well and has so far. Fred, on the other hand, has had his Devcon only fitted barrels shoot loose, but he also shoots those a lot.
Tim