My 500A was the same when I got it, I had a noticable gap at the rear of the hanguards. Not as big as the one in the pictures though. Just not perfectly flush like you want a $300 add on to be.
I did a bit of careful scraping, and carving with the old pocket knife on the two 'tits' that look like they are supposed to seat on the bbl nut. Got the hanguards to where they almost met then took a big roll of duct tape and smacked the rear of the unit a few times to crush fit them when they were mounted on the carbine(since that was apparently what the intention was, plus it made me feel better).
No damage to the weaponslight and they fit perfectly, are nice and tight even after being taken on, and off a few times. I will try post pictures at some point. They may even be made to gradually 'wear' in but it would probably take forever even if you carried the rifle all the time for that to happen. I think it really just depends on what 'oclock' you bbl nut is at. A buddies went on flush first time and the 'tits' on his are not mashed at all (some guys have all the luck).
A note in the manual about this would have made me feel better when I was wailing away with that roll of duct tape though :)
Carbine is a Bushmaster m4A3, with carrying handle still mounted, and Trij reflex. The M500A unit is one of the older one without LEDS :(
HoG