I am planning on getting a Lucas bore guide but have a couple questions before I do. I know that the guides are made to fit the specific chamber size, but are they made so that a .308Win bore guide is the same for all .308Win. chambers? Is the only difference the length of the guide? Or are they made so that a .308Win Accuracy International guide would have different chamber dimensions than a .308Win Remington 700? Thanks for any help you can give me, and please go easy on me if this is a stupid question.