I picked this book on Colt Machine Guns this past weekend. I'd never seen it before and the book dealer is retiring at the end of the year, selling out so everything was 50% off. It includes all .30 and .50 caliber, water-cooled and air-cooled and the BAR and Colt Monitor. It's not a history but a technical guide and manual more than anything else. I thought it's a neat book to have and 50% off made it easy.