Ruger Blackhawk and Vaquero Vaqueros come with a "color cased" and blued finish or an overall gloss stainless steel. Grip shapes are "bird's head," Bisley, and traditional. Barrel lengths are 3 3/4, 4 5/8, 5 1/2, and 7 1/2 inches. Vaqueros are available in .357 Magnum/.38 Special, .44-40 WCF, .44 Magnum/.44 Special, and .45 Colt. These guns have an overall length of 11 1/2 inches and weigh 40 ounces. Vaqueros are a favorite with Cowboy Action Shooters. Ruger Vaquero - Wikipedia, the free encyclopedia
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Some of the best referrences you will ever find on Ruger guns, production numbers, variations, etc. are the RENE (Red Eagle News Exchange) referrence manuals. A wealth of information for not alot of money. The guides are provided to new subscribers to the quarterly newsletter, and well worth the effort for anyone interested in collecting Rugers.
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I forgot; measure from the cylinder face; to the end of the barrel +- Thread count will be the differences