What does the axel length have to do with the purchase i was looking at the PSE Brute X and from what i read looks like a nice strater bow and a great price. It is adjustable for draw lenght and all question they have AXEL-AXEL 31" Is this something i need to undestand before purchase or is it a number that only really matters once you get more advanced. like a M-16 is a nice rifle to qual on since it is bigger and a M-4 is harder becase it is a smaller rifle?