Not sure if this is something that can be tracked, but I've always been interested in the kills attained with various ammunition. The key example that comes to mind is the USAS12 and its controversial Frag rounds. I don't tend to use them often, not a fan, but I do like the gun with its stock Buckshot and have fooled around with the other types a little. Being able to hover over the gun (or some other form of implementation) and see just how I'm using guns with various loadouts would be interesting.
I don't think that data is availabe, but i will do some tests.