I have had 3 and currently have 2 (300 and 325). For the 300wsm the price of ammo is not much different if you compare the same ammo, ie same manufacturer, same bullet, same line (ie federal premium tsx against fed premium tsx). From what I have seen it is usually under $5 a box difference between the 300wsm and the 300 win mag. You can't really compare price of 270 win to WSM that is like comparing the price of 30-06 to 300 win mag. I will say that there is not much for cheap ammo to be had, the winchester grey box can be tough to find if you want cheap factory loads.