Iam a newb so please bear with me. I have a rem 700 sps aac-sd and currently running an aluminum weaver one piece picatinny base with the rings that came with my cheapy bsa tactical weapon 3-16x44 scope. I have just aquired a nikon 4-12x40 bdc scope and was looking to upgrade my base and rings as well. I am looking at a badger steel 1 piece picatinny base and burris extreme tactical rings. My question is, the badger bases on midwayusa have options such as 20 moa elevated, what does this mean? Also what height rings would I need? Should I keep the Base that I have now and just Buy Rings? Any advise is appreciated thanks.