This seems like the right place for this topic - saw a photo in the 1976 Jane's Infantry Weapons (p. 256) of a triple magazine arrangement ("assault tri-mag") for the Open Bolt M16A1 Squad Automatic Weapon.

To support the weight of three loaded 30 round magazines clipped together, it had stamped metal spring that rested on the outboard edge of the magazine release - basically providing another friction point to secure the magazines.

So I went looking to see if there was a photo to share and found something better - the original drawings that were part of the Patent submission.

https://www.google.com/patents/US4057003

https://patentimages.storage.googleapis.com/pages/US4057003-6.png

https://patentimages.storage.googleapis.com/pages/US4057003-5.png

Sooooooooooooooooo.... which one of you suppliers is going to crank out some of these?

http://www.redi-mag.com/index.php?l=product_list&c=9 ?

Similar concept, but sort of over-engineered?

Original design looks like folded spring-steel and a couple of tack-welds. So easy, even an AKsmith could do it.

The non-linkedness was getting to me:  https://www.google.com/patents/US4057003