I have purchased a NIB 3rd gen Glock 21. I have (7) other Glocks. The 21 when you shake it side to side the slides appears to be a little loose and rattles back and forth, not much but noticable. Is this normal. When you pull the slide back and set the trigger it stops. This is not the striker sound but the slide fells like it has a little give. I believe this is just a spec tolerance issue. I don't think it hurts a thing. Am I correct? THANKS!!