Can't add anymore that hasn't already been said about having a well round gun library if you are going to be serious about investing in the antique gun field. At today's prices, you better be educated about the purchase you want to make, or it can be costly! That being said, any book you can add to your library written & researched by Charles Pate is worth the investment, 10 fold. Research books, like anything else, you get what you pay for. IMHO, Charles is head & shoulders above his peers & he has personally contacted me about a rare Colt conversion that I have, that a total of 50 were modified by Colt. I collect weapons from the Post Civil War cavalry including a S&W Model 3 American & is one of 1000 purchased by the Army & does have the oil hole. I don't know if Charles has this number, but is free to add to his list. It is #830 and all inspector marks are present uncluding the tiny US on barrel.