I came across this blog post... I though it was really good
http://booksbikesboomsticks.blogspot.co ... 1930s.html
Highlights are below
I've been following the new quad stack ar-15 and prototype Russians ak-74 quad stack mags for a while, thinking they were new and novel... guess what they aren't
From the 1980's
http://en.wikipedia.org/wiki/Spectre_M4
From the 1930's
The sumi also used them too, called casket magazines
http://en.wikipedia.org/wiki/Suomi_KP/-31
I had always assumed glocks trigger safety was the first of it's kind.... nope!
from the 1930's
http://nramuseum.com/the-museum/the-gal ... istol.aspx
Interesting.
More are in the blog.