I must admit my heart sank a little reading your post. I own a full sized M&P 40 and recently purchased a Storm Lake 40 to 9mm conversion barrel. It is the 4.95" threaded barrel (gonna have to break down and buy another AAC product) and hadn't had a chance to shoot with it yet. Ran 103 rounds of various brands of factory ammo through it with zero issues. No FTF, FTE, or any problems with slow, intermittent, or rapid fire. So far I couldn't be happier. After 900 more rounds like that and this weapon system will get to stay and get listed in my trust.