I like to get my hands on as many different m1 carbine books I can, This way I can see how many agree. All Harrison knowledge can`t be all wrong. And I`m sure he`s right on a lot of things,maybe not as right as others , So you take from them all.And learn what you can from books and forums. Ask a lot of stupid questions and hope you get a smart ans.At least that`s what I do