I understand the AR-57 upper is "legal" as long as it is used with a pre-ban (or 10 round) mag and the flash hider is changed to muzzle brake:
http://www.impactguns.com/store/AR-57 UR.html
But the question is - are there pre-ban mags available and/or 10 round mags available that would fit this - or a PS90?
According to Wiki the PS90 entered service in 1994 - which would put it on the hairy edge of high cap mag availability (pre-ban)
http://en.wikipedia.org/wiki/FN_P90
http://www.impactguns.com/store/AR-57 UR.html
But the question is - are there pre-ban mags available and/or 10 round mags available that would fit this - or a PS90?
According to Wiki the PS90 entered service in 1994 - which would put it on the hairy edge of high cap mag availability (pre-ban)
http://en.wikipedia.org/wiki/FN_P90