The 30-06's ability to penetrate is vastly superior to that of the .223. I have no online data to support that, merely my own observations of the targets.
I do recall that the '06 was designed to be able to penetrate 16 inches of oak, The plan being able to get through to hiding opponents. Of course that is with hardball, not the soft points most folks find and fire in 30-06.
Brother Browning's design was to build a man portable, fully automatic broom that would sweep the fields between the lines of WWI Europe. I recall reading someplace that the original plan including teams of Browning Riflemen sweeping the field, firing burst each time their right feet hit the ground.
I've seen a belt that was described as a "BAR Belt" with mag pouches along the circumference, and a cup for the butt of the rifle. Although I can find no pictures of that particular belt, all I see are the WWII versions like
This.
I figure a lot of the changes in US weapons had to do with changes in the world. Few of our soldiers are the hunters that their great grandfathers were. Fewer are the farmers that woke at sunup worked throughout the day on a field behind a horse doing hard labor.
A rifle that would penetrate though heavy walls and still have the energy to kill would be a benefit in their world, one without newspapers or news-crews constantly watching. A world where most of their adversarys and comrades were bearing bolt actions, where an M-16 can likely empty an entire magazine before a clip of 30-06 was run through. A time where the lighter recoil wasn't a neccessity, they had to jerk a bolt and ram it home before they could fire again. Hopefully something not required with a modern combat rifle.
Please also take a look at the weight of a BAR, it isn't a puppy you are just going to swing over your shoulder and enjoy carrying. To us, it's a bear to lug, although compared to it's contemporaries it is light
http://www.rt66.com/~korteng/SmallArms/browning.htm
I believe that the larger caliber, the longer range, and the greater penetrative power of the 30-06 would make it better suited to the open fields of much of Europe. However in close confines, short ranges, close contact a small gun, much like the SMG's and light carbines would be advantagous. I figure the M-4 is just the newest compromise weapon we've fielded. I bet we've all read of the M-14 being fielded again in afghanistan where the ranges are greater.
Jerry Pournelle wrote several books about the future, Prince of Mercanerys being a favorite. They bore rifles that wouldn't be that far out of the field of design that our fathers had. What goes around comes around.
(I'm off to work, first day back from vacation, forgive the typo's I'm running late again

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