Ok, I've set back as a guest and have read all about which gun for elk and have decided I will buy a 7 mm. I will admit I know nothing about rifles! What is the difference between a 7mm WSM, Remingtom & Weatherby Magnum, Ultra Magnum, SAUM, Express? What do I buy? Do they all shoot the same cartridge? I don't think so, but I don't know for sure so that is why I am here! Which would be the best for Elk? Help me out please! Thanks!