Went to a range today to compare a few pistols (1911, Glock 21, S&W M&P, and XD, all in .45 acp) and shot my tightest group with the M&P. The only problem was that the gun was malfunctioning, after about 80% of the shots the slide would lock back like the magazine was empty. It was a range gun, so probably neglected pretty badly, but when I told the guy at the counter about it he said that the M&P has a reputation for having problems with the slide lock. My next best group was the XD but M&P shot significantly tighter. So how common is this? Any M&P .45 owner have this or heard of it?