The S&W model 10 with a 3" barrel was quite prized. I have a friend that bought his boss's model 10 he used when he was an agent. That model 10 was a 3" pencil barrel the only one I have ever seen. I have seen many 3" heavy barrels but not another tapered barrel. I also know agents were allowed to carry any 6 shot revolver that was at least .38 caliber. I have heard of many agents who carried 357 Magnums of different models. I also know of one former agent who carried a S&W model 57 41 Magnum. How do I know it was a 57? He did a presentation to my class when I was in Junior High School back around 1973.