I want to put a rail on a Rem Mod 7 so I can have more flexibility in how far away form the eye I can mt. the scope. Since I have never used rails would someone please tell me how I select what I need. What is the significance of 10 MOA, 20 MOA, OR 30 MOA? What does this do and how do I know which I need. What are th pros & cons of Aluminum and steel? Other than a weight difference? Are there ones significantly better than others and how do I tell which are best? Thanks for any and all input.