From the books I have read, at the time of the adoption of the M14, the Infantry school did not want magazines because they had gotten used to the enblock Garand clips. The Infantry school, in 1952, wrote a memorandum to the Chief of Army Field forces recommending the elimination of 20 round box magazines for any service rifle. Any and all service rifles! You can find this on page 65 of
The FAL Rifle and page 119 of
US Rifle M14 from John Garand to the M21 The user declared that box magazines weighed too much, had limited durability, and caused battle field loading problems, might have been too expensive, etc, etc. The basic problem was that box magazine was not an enblock Garand clip.
The user, if you ever meet and talk requirements, the Infantry likes what it has, wants something better but only a little different, and totally rejects revolutionary change. A box magazine was too much change.
Reviewing early M14 literature and training tapes, the developer installed a stripper clip slot on the top of the rifle, and the magazine was called "
semi detachable".
I saw familiarization films showing the loading of the
"semi detachable magazine" with stripper clips in the rifle. I have tried this, and it is a thumb buster. When the M14 was introduced to civilian target shooters at Camp Perry, they were required to load the thing with stripper clips during the rapid fire sequences. All of the written reports indicate how difficult that was. I never saw anyone ever reloading a M1a with stripper clips, through the top of the rifle, everyone dropped the magazine, and put a fresh one in the magazine well.
Stoner had to have heard it all, wanted to keep the user happy, and he designed his magazines to be cheap, light, and early literature called them disposable. The Infantry got what it wanted, except for the part about the magazine being unreliable, because cheap, lightweight, aluminum magazines have lip spreading issues. I think I saw a steel AR15 magazine, a bud was selling the thing but I did not want it. It must be a real trick to make a steel magazine that fits within the receiver envelope of the AR15, because you don't see the things around. The only Colt magazines I have seen are aluminum 20 round and 30 round.