OkieCruffler: The gun came with my wife. She bought it for HD before we met but never bothered to test fire it. Fortunately, she never needed to use it: it might have gone 'click' instead of 'boom' at an inopportune time.
To be fair I think this problem probably only affected a small amount of guns but reading stuff around the web convinced me it wasn't only my gun.
Thread about my gun here: