I put about 200+ rounds of various ammo through my new S&W M&P Shield 9mm & the only malfunction was its failure to lock back once & that was on the very 1st mag. I went to the range y'day & 4 out of 8 mags I got a failure to lock-back. ..just wondering if this is common with the Shield & if maybe it should be sent in to S&W? The gun is very clean & lightly lubed. And, no, I don't limp wrist it. The hg has never jammed.