Looks like staple gun that a carpenter might carry.
The Ruger Factory hi capacity mag cannot keep up with the cyclic rate of your weapon. They have a drop in kit you may obtain from the manufacturer. Simply go to their website @ http://www.zipfactory.com/pages/zipquickview.aspx
You should be able to t.c.o.b. from there. Good Luck & Good Shooting, Ddoc110.