Rugerlvr . . .
Watch the hammer of your M28 when you release the trigger. Notice how it rebounds away from the firing pin. The gun's rebound slide cams the hammer back when you release the trigger. A moderate blow to the hammer won't do anything because the hammer motion is blocked by the rebound slide. A really hard blow to the hammer can break the hammer stud, which would allow the hammer to move forward. This is why S&W added the hammer block, which blocks the hammer from the firing pin unless the trigger is pulled.
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On a single-action revolver with a transfer bar the hammer is designed in such a way that, although it impacts the frame, it cannot reach the firing pin. When the trigger is pulled, the transfer bar is interposed between the hammer and the firing pin. The hammer hits the transfer bar, and the transfer bar hits the firing pin.
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The New Model single-actions by Ruger, in addition to a transfer bar, are designed in such a way that when you open the loading gate with the hammer forward the cylinder bolt is retracted so you can rotate and load the cylinder without any manipulation of the hammer.
When you load an Old Model Ruger with the transfer bar upgrade, you still must draw the hammer to half-cock in order to load, which means you need to manually lower the hammer after loading. Draw the hammer back to full-cock, get contol of it with your thumb and pull the trigger. As soon as you have lowered the hammer beyond the full-cock, get off of the trigger. This will retract the transfer bar and nothing bad will happen if the hammer slips from under your thumb.
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To correctly load a traditional single-action (no transfer bar) as a "five-shooter", load one round, skip one chamber and load the next four rounds. Immediately after loading the fifth round draw the hammer back to full cock and then manually lower it with your thumb. It will come to rest over the empty chamber.