Re: New flat top question.
Mine cam with sights but removed them put a set of Magpul flip-up sights and a red dot on mine. Did not care for the removable one that came with the gun.
Re: Loose fitting magazine fix
I used sticky velcro. Cut ttwo pieces and stuck them to the top of the magazine infront and behind the extention, put them in the gun and let them set for a day. No issues mag fits tight no rattle