No, then you'd have 20,000 rounds in the tail gun...
And what good are the other 19,400 rounds of ammunition when the only people who don't attack from the dead 6 position are the guys in the 262's, 152's, and 190-A8's smashing your bomber group apart from the front where you only get 1/4 of a second firing time? The only guys who don't attack from the 6 O'clock are the guys who usually attack from such angles as to make defensive fire useless.
IMHO, the tail gun should be reloadable, but at a price. One belt of 100 rounds at a time, requiring 30 seconds to reload after you fire out your ammunition. Think about it. The tail gunner has to get out of his position, while wearing a breathing apparatus, flack jacket, heavy clothing, gloves, etc. etc. etc. Walk/crawl/waddle up to the top/nose/waist gunners. Open their box, grab the ammunition, walk/crawl/waddle back to his position, open his box, throw the ammunition in, toss it on the gun and chamber a round. I'd be surprised if that's do-able on the ground in 30 seconds; let alone at 20,000 feet, in the cold, with someone shooting at you, with turbulence, flack bursts raining all over the sky, and so forth.
100 rounds might not be much, but there've been times where even 5 bullets would've saved my bomber, and there are other things you can do while waiting to reload. Pitch her up into auto-climb so the top gun can get a shot. Initiate a violent left/right turn while in the waist gunner position with the rudder pedals so they can get a shot. Not sure if the 17 can, but I know the 24 can perform an Immelman, scare the hell out of pursuing fighters be ho-ing them. (Not sure if I have film of it, I was in a Wirble watching an enemy 24 on the deck playing around, I'll need to look.)
