medicman816 is closest based on several documentaries that I recall seeing in the mid to late 1990s. Dr. William Atwater, curator of the US Army Ordnance Museum at Aberdeen Proving Ground, was featured in several Weapons At War segments that discussed the introduction of the M16 rifle into service with US Forces in the early 1960s. The shows were on the History and Discovery Channels. Dr. Atwater, as I recall, described the adoption of the 30 round mag being based on Army and Marine Infantrymen having seen the 30 round mag for the AK47 and demanding 30 rounders for the M16.

I searched both History and Discovery Channels for DVDs on the topic but did not find the specific videos. Dr. Atwater's wikipedia site does mention his participation in these types of videos.