You asked for it...I know that they exist....Grease Gun and Thompson Mag .45ACP Ar-15's or should I say AR45.

Here's a link from another forum:
http://www.oa2.org/forums/viewtopic....=thompson+mags

PM TangoChaser on that forum

The Thompson system uses a rail on the reciever, the consensus over there is go with the grease gun mags.....personally I'm happy with my sten gun mag set up.