STL Search: AR10 300WM Lower

Hey, I want to put a 300WM upper on an AR10, but I know that those bullets are too long to fit in the magwell of a short-action AR10 like the Hoffman Tactical AR308 or the BUBAR-10. So does anybody have a long-action AR10 lower STL? I would greatly appreciate any advice, I'm trying to make something for big game.