when you put it away, lock the slide back for at least 24 hours.
HK's (at least all of the ones I've bought new) have had stiff recoil springs that need to "season" in to their intended spring rate, then hold it until the next epoch arrives. :D
Rules to live by: 1. Eat meat... 2. Shoot guns... 3. Fire... 4. Gasoline... 5. Make juniors