No longer have my old email account (and I moved) so I re-registered.
It started a long time ago but with RPD mags.
"The SEALs also would take RPD drums that were captured and cobble together mounts in the field to use them on the Stoner."
Link here:
http://home.comcast.net/~sfischer397/stoner/feed.htm
Armorers in vietnam would also fabricate AK mags that fit M16's. The franken-mag would hold more ammo, and were used by the Point Man. The logic behind a larger magazine capacity would be reaction by a higher than normal volume of fire when spotted or ambushed. The one magazine was used, then use of normal capacity used thereafter.
Pics of the mags are rare, but there are a half dozen pictures floating on the web...
http://img90.imageshack.us/img90/6707/akm1611.jpg
http://t2.gstatic.com/images?q=tbn:A...fkinw84iIcbaqE
http://s171.photobucket.com/albums/u...RVNofficer.jpg
http://www.hunt101.com/data/500/23482925vy8.jpg