Technically, the USS Pennsylvania. I believe USS Wyoming fired more but had been reclassified from battleship to gunnery training ship, and thus was no longer truly a battleship.
My answer was the Wyoming. Interesting about the reclassification, I'll have to look into that. Thanks
http://en.wikipedia.org/wiki/USS_Wyoming_(BB-32) She was reclassified from BB-32 to AG-17 in 1931. As part of the conversion, 3 of her 6 main battery turrets were removed, as well as her armor belt. She might have lost boilers and shafts as well but I am not positive.