Shotgun range-15 or 20?

[Basictree]

I'm a bit confused here, and searches did not yield any results to my inquiry, so I hope this thread clears up some of that confusion I have over the shotguns range. When I mouse over the firearm it's self, I read 20 range. But then I moused over the ammo, and the tool tip read 15 range. So, there is my conundrum. Is the shotguns range 15, or 20?