http://i.imgur.com/0OqH3RU.jpg
This photo made me think "Even if every shell killed only 1 person". But would every shot in that photo be aimed at an active enemy position? Or were areas bombarded not because the enemy was there or moving into the area, but just to keep them out? For example, even though the enemy is not there, if we bomb the fields on our left flank continually, we are protected?
You'd never "bomb your left flank" to keep it protected. In WW2 a bomb, as it were, was a strategic weapon, with some limited tactical benefit via dive bombers. You bombed factories, population centers, and oil refineries.
That aside, while I won't give a complete answer because I'd probably be able to write a book with it, lets put this in some sort of context:
The US Chief of Ordinance, Lt. General Levin Cambell said that the US war machine furnished all arms of the US armed forces, in addition to 43 other countries with 47 billion rounds of small arms munition, ~11 million tons of artillery ordinance, 12 million rifles and carbines, 750,000 artillery pieces, and 3.2 million military vehicles.
But you'll never get a straight answer because a fair number of deaths are not going to be caused by munitions. You have to account for illness, post-wound deaths, sharp instrument deaths, ect.
