My new S&W shield performance center did this. I can remove the mag and pull back on the slide and slide will lock back without slide stop engaged. I think it is a rsa issue not a barrel issue. As when I took my gun apart to clean factory oil off it before shooting recoil spring was try to over ride the guide rod end. S&W has some terrible quality control on their rsa assemblies. Not sure who makes them for s&w but they aren't the best machined guide rods or springs.