"...you continuously change shoulders when moving with a rifle..." Not in The Queen's Service you don't.
"...The No. 5 was for the..." Originally used by the Paras, but not designed for 'em. It was designed for use the jungles of the CBI Theatre.
The "rubber" butt pad is India rubber. Same as a lacrosse ball and very close to a hockey pucks and a few igneous rocks. snicker.
"...somewhere in the hallowed halls..." Yep. It's what happens when a civil servant gets an idea and is allowed to run with it, no matter how stupid.