Army Live firing on Salisbury Plain. When and where can I go to watch some?

Why on earth would you want to do that? I quit the army in the early 80's. I recall "A day at the ranges" (I know it's a dreadful pun) as being among the more boring of the various military pursuits. I can only suppose that your life must be short of excitement. Ranges are closed to civilian access when live firing is taking place