Seawolf.
The ten round magazines fit and work great with this set up . Other options are 15 round mag or if you can find one they made a long time ago a 30 round barrel type mag that will work, but talk about a boat anchor to shoot!
Very Heavy! mag looked like something you would use on a Tommy Gun .
I forget the name of the manufacturer.
Last I saw Mechtech had a waiting list on their website to order these things
