David: Very clear pictures of the early mechanisms. Although not mentioned above, the pictures also show the difference in the earlier cylinder stops, which simply pivot about a pin without the reciprocating and pivoting motion of the later cylinder stops which caused the appearance of the 5th screw in the trigger guard.
These early guns also used a single stage double action system where the double action worked entirely off the sear strut on the hammer. The difference between the early and later double action can be seen clearly in the picture of the gun with the rebound slide, where the double action starts on the sear strut, then transitions to a notch in the rear of the trigger working directly on the hammer. That is what gives the later S&W revolvers the super smooth double action.

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Tom
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