I am planning on building a long range rifle with a Savage action in .308. My understanding is that the .243 was built around the .308 cartridge. If that is true, doesn't that mean I can take a used .243 action and, having the same size bolt, put a .308 barrel on it and it'll be the same thing? If that is the case, this makes it a little easier to find a cheaper, used action since I have more calibers to choose from. Is my thinking correct?