Awastatyme
.270 WIN
A company called Black Ace Tactical has come out with a replacement receiver for the 500 and Maverick 88 that will let you use Saiga 12 mags. They also sale full shotguns using those receivers.
http://www.blackacestactical.com/#!product/prd3/1649145685/pro-series-5-retro-receiver-kit
http://www.blackacestactical.com/#!product/prd3/1649145685/pro-series-5-retro-receiver-kit