Welcome aboard from Iowa! The differences between makers question could fill a page or two and then leave out some details. There are now differences in patterns even within the same maker. Start with the build articles on the forum page; http://308ar.com/category/projects/ Browse through the tech subforum; http://forum.308ar.com/forum/9-308-ar-technical/ Work the search function here; http://forum.308ar.com/search/ Read, read, and read some more. You need to decide what you are going to do with the rifle, what are your expectations for it? Do you have experience with the AR 15? Most of all before you order or buy any parts post a parts list and the guys here will scrutinize it for possible issues or suggest improvements.