You are giving me a bit more credit than I deserve. I only know what the Standard Catalog of Smith and Wesson says about it.
"Model 14: The K-38 Masterpiece Single Action
Caliber: .38 S&W Special*. As described above but deletion of internal parts allows single action only. Pulling the trigger only rotates the cylinder but does not lift the hammer. Available with wide or standard width hammer and trigger. Manufactured c. 1961-1982."
This is a Model 17, not a Model 14, but except for the Model 14 being a centerfire vs a rimfire Model 17, the lockwork is the same. The upper arrow is pointing to the Double Action Sear. It is a spring loaded, lever pinned to the hammer. The lower arrow is pointing to the Double Action Sear Strut on the trigger. Normally, when the trigger is pulled double action, the Double Action Sear Strut on the trigger shoves the Double Action Sear up, pushing the hammer back. At some point the strut will slip off the sear, and the hammer will fall. As the hammer falls the Double Action Sear is shoved back into the hammer, allowing the hammer to fall all the way. This happens if the trigger is pulled double action or if the hammer is cocked single action and the trigger releases the hammer to fall. In either case, the Double Action Sear is shoved out of the way, but pops back ready for the next double action shot. I suspect all S&W had to do to make the Model 14 a single action only revolver was to eliminate the Double Action Sear from the hammer assembly. Then pulling the trigger double action would cause the hand to rise and rotate the cylinder, but the hammer would not move.
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I have a bunch of old dealer pricing guides going back many years. The guide from 1961 shows the K-38 Masterpiece Single Action (Model 14) selling for $90.00, the K-38 Masterpiece (Model 14) (the regular model) selling for $81.00. I seem to remember kits were available to turn a standard Model 14 into a single action only model 14. Probably just a hammer without the Double Action Sear, I don't know if a new trigger was supplied or not.
*When they say 38 S&W Special that is the same as 38 Special, S&W just wants every body to remember they developed the cartridge.
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The same with 44 Special.
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