"Jumping" the slide catch when a loaded mag is inserted is not a feature designed into the gun. Virtually all double column mag pistols can be made to do this if you slam the mag in hard enough. It may look way cool, but it is not what you want to happen for several reasons. If you are not careful with your trigger finger, for instance, it can...and has...lead to AD's.
The "free play" in your trigger is there to insure that the mechanisn works correctly under service conditions by allowing everything to correctly re-engage when the slide slams home after firing. H&K sells a target trigger assembly for around $100 (plus whatever it costs for an install) that can fix this to a great degree, but ,typically, target parts are not something you would want on a service type weapon.