I am a noob trying to learn and I can't seem to find it by searching so here goes. What is the advantage/reason for having a 0, 20, 30 or 40 cant on a rail? What does putting a canted rail on a gun do?? And how do you know what size to get. Again, I'm a noob looking to get a good rail for my brand new 700 AAC-SD and Bushnell 10x40 and wondered what the difference was or which one to get. Thanks.