Hi all, I just picked up a G21 Gen4 about a month ago and have found a slight issue with it. The slide does not lock back if the mag is empty. When shooting it upon last shot it usually does lock back but I have had two instances where it did not. The born date on this gun is 01/27/12. One more thing is that I am shooting 230gr factory reloads but that does not explain why it won't lock back on an empty mag. Any suggestions?