An oldtimer at my club Bought a FN 5.7 last year today he was inquiring about getting an AR chambered for the 5.7x28. I know there are specialized uppers chambered for this http://www.botachtactical.com/pwa57x28upper.html But because it is a 50 round magazine it is illegal in MA (or at least the magazine is). Does anyone know of a 5.7 upper that is fed by a standard style magazine in a conventional manner and configuration so that it would be MA compliant?