I do not believe that Ruger ever made a convertable 45C/45ACP in the OM Vaquero. Several of us have managed to find 45ACP cylinders on GunBroker or Gun Parts Corp (Numrich Arms) and had them fitted to the Vaquero. The Blackhawk cylinder is interchangeable to the Vaquero one and usually is a drop in. It took me less than 15 min to fit the 45ACP Cylinder to my Vaquero and had my 'smith to check timing although I was sure it was OK. Off a rest, my 45ACP Vaquero wll shoot 230 gr FMJ rounds into 11/2 groups at 25 yards. BTW, I converted a 44-40 Vaquero to 44 spl, by fitting a used 44 Mag cylinder purchased online. Fit and timiming are perfect, but have not fired it yet. Ruger manufactured all their 44-40 pistols with the same bore diameter as their magnum Blackhawk and Vaqueo barrels. It's a shame Ruger discontinued the 44-40!.