Watching the news and seeing footage of the soldiers fighting in Iraq, I’ve noticed that they hold their rifles with the butt placed atop the shoulder rather than the way I’m used to seeing it done - with the butt placed against the front of the shoulder sort of in the ‘armpit’ area.
Why?
If one is firing from behind a wall or other type of cover, you can get the rifle barrel parallel to the ground this way without “overexposing” yourself.
On the shoulder - never the armpit - or just inside a bit closer to the collarbone is normal. A shoogter can get away with the unorthodox style as the M-16/M4 has fairly mild recoil and is still pretty easy to control.