The following is a relatively easy-to-read article from Jeff Gurwitch, a contributing author to the blog at skdtac.com. Informative, technical, all while remaining concise – the complete post gives a good explanation on why US Army SF adopted high ready techniques for CQB (body mechanics): http://blog.skdtac.com/2014/12/27/high-ready-or-not-here-i-come/.
“When it comes to techniques and methods employed in tactical shooting there are, in many cases, certain developed solutions to very specific tactical problems. Unfortunately, when passing on these techniques to others, sometimes the “why” of something being done a certain way is poorly explained or left out altogether. As a result, all too often you see techniques being taught or employed incorrectly or being adopted as an all-around shooting method instead of as an answer to a specific problem.
One such technique that is very misunderstood within the tactical shooting community is the High Ready method of holding the rifle. What has been lost, or not understood about the High Ready, is that it is an answer to a very specific problem within CQB. Often it’s explained that you’re automatically in the ready position to muzzle strike someone or be able to run faster with the gun (both are true), but these are not the main reasons behind the use of the High Ready.”
I’m no professional doorkicker myself, much less an adept/experienced CQB airsofter in the make-believe BBwarz world that I find myself in, hence why I find this a great answer to the “why” behind high ready, which I never really understood.