Is the 300 prc really just a necked down 375 ruger? I hear on a lot of pages that the prc is 'based on' the ruger but I would guess that means they are close. However I suspect if it were the same just necked down, I would have read somewhere that was the case. Anyone know the diff? Only some of my reloading books have the 375 ruger, and none have the 300 prc.