I have done the same thing many times. It only takes a little work to get Ruger cylinders to interchange. ALL Ruger 45s are the same size, both Old Models AND New Models. I have a 44-40 Vaquero I fitted a 44 Mag cylinder to. I also have a 44 Spec Blackhawk but a 44 Mag cylinder is way too large to fit. That is why I want to fit it (the 44 Spec) with a 44-40 cylinder.I'd like to comment if I may about the Ruger 44-40/44 spl-mag question. Several years ago I purchased a 51/2 in. Ruger Vaquero, ANIB, at a local firearms auction for a very good price. Wondered if a old Blackhawk or Vaquero 44 Mag cylinder could be fitted to this revolver. I called Ruger Tech Service and found that Ruger used the same barrel on both their 44-40 and 44 Mag pistols. With that knowledge, I starrted looking around, and finally found an original Blackhawk 44 Mag cylinder in excellent condition. With a minor bit of fitting . it worked perfectly in my 44-40 Vaquero and the fit and timing were perfect. To top things off, it turned out to be an excellent shooter, giving me 11/2 '' groups at 25 yds. I'm mentioning all this, since you could do the reverse; buy a Vaquero 44 Mag revolver, and locate a 44-40 cylinder for it. Solve's your problem! BTW, I did the same thing wit a Vaquero 45 Colt revolver, fitted a 45 ACP cylinder to it for a another excellent shooter for dual catridges.