My latest in a long line of S&W pistols is an M&P 22 compact. I've enjoyed it thoroughly, but the protector on the threaded barrel comes loose constantly. Made a wrench to fit the narrow flats on the bell, but no matter how tight I try to make it, it is loose in a few shots. This last time I cleaned the threads very thoroughly with alcohol and then coated it with Loctite 242. If that doesn't work, I'll try 290 next. Anyone experience this problem or have other ideas for a fix?