I'm looking at the listing for Champlin arms and they have a lang 450/400, looks great. Going to take a short drive and take a look at it. How does one buy a double rifle what should a person look for in double rifle. I understand that Champlin arms has staff that are very knowledgable in this area, is there a book on this subject, I like to research my guns before I buy them talk to someone who has one.