Howdy
At the top of this photo is a Three Screw 44 Magnum Flat top Blackhawk. At the bottom is a New Model 45 Colt Blackhawk. Notice the New Model has two pins for the hammer, bolt and trigger to pivot on, rather than the three screws of the older model.
The mechanism of a Three Screw Ruger was very similar to the mechanism of a Colt Single Action Army. The leaf springs were replaced by coil springs and plungers, but other than that they functioned the same as a Colt. Four clicks when the hammer was cocked. Putting the hammer at half cock allowed the cylinder to rotate for loading, just like a Colt.
Here are the parts of the lockwork.
In the early 1970s Ruger completely redesigned all their revolvers. This was because they lost several, not just one, expensive lawsuits when their revolvers accidentally fired when dropped on their hammers. Just like the Colt Single Action Army, if dropped on the hammer, there is a good chance the revolver will fire if a live cartridge is under the hammer. Here is a photo of the lockwork of a Colt SAA. The two arrows are pointing to the tip of the trigger, known as the sear, and the so called 'safety cock notch' on the hammer. Notice how thin the sear is. When the hammer is pulled back slightly so that the sear pops into the 'safety cock' notch, the firing pin is withdrawn from the primer of a live round under the hammer. This was designed to make the revolver safe to carry fully loaded with six rounds. However long experience has shown that if a Colt is accidentally dropped on its hammer there is a good chance the sear will break off and the force of the blow will drive the firing pin into the primer of a live round under the hammer with enough force to fire the cartridge. So anyone who is familiar with a Colt knows to only load it with five rounds and leave an empty chamber under the hammer.
The old Ruger Three Screws suffered from the same problem. Go back to the photo of the Three Screw lock parts and notice how thin the sear is. They were perfectly safe if you remembered to only carry one with an empty chamber under the hammer. If you fully loaded it with six rounds, you had to be careful not to drop it. Eventually enough of them were dropped that Ruger completely redesigned the mechanism and included a transfer bar to transfer the hammer blow to the frame mounted firing pin. Opening the loading gate frees the cylinder to spin for loading, rather than putting the hammer at half cock the way it was done with the Three Screws or a Colt. When the hammer was at rest, the transfer bar with drew and the hammer could no longer contact the firing pin, so the New Models were completely safe to carry fully loaded with six rounds.
This is a photo of the transfer bar in the 45 Colt New Model Blackhawk pictured above. The hammer has been cocked, and the transfer bar has risen up so that when the hammer falls it will strike the transfer bar, which will transfer the hammer blow to the firing pin, firing the cartridge.
This is a photo of the lockwork of the New Model Blackhawk. The long, thin piece attached to the trigger is the transfer bar. When the hammer is cocked, the trigger rocks back slightly raising the transfer bar up so it will be positioned between the firing pin and the hammer.
Long ago Ruger offered that it would convert any of the old Three Screw Blackhawks for free by replacing the mechanism with new parts that included a transfer bar. Generally speaking, the action of a converted Three Screw is not as nice as the original Three Screws were.
If the Three Screw has been converted to having a transfer bar, I wouldn't touch it myself. I have several unconverted Three Screws and I always load them with five rounds and leave an empty chamber under the hammer, no different than I do with a Colt.
If you feel comfortable only loading five, and leaving an empty chamber under the hammer, go for it.
If not, go for the New Model.
. I'll settle with a NM.
