Howdy. I have noticed this condition with most HK 91's - four out of my six for example, to include two new in the box - so to me it is pretty normal. I like a small dab of good 'ol fashioned rubber cement on the front surface of the trigger housing and/or rear surface of the magwell ( where the two contact each other ) and the slop is gone. Let the cement dry for about 20 minutes before you re-assemble and it will stay put and do the job for, well a long, long time and much dis-assembly / re-assembly. The minute you no longer want the rubber cement on your weapon it will rub off just with thumb / fingers with zero trace of ever having been there. This little trick also works well for handguards with a little slop in them, be it fore and aft or up / down play. Just apply cement carefully to the handguard surfaces that interface with the weapon itself. Take your time and you can get a neat, professional result that is out of sight / out of mind. Hope this helps.