The hammer block is a drop safety. It is there in the event the gun is dropped on the hammer spur hard enough to shear the pivot pin the hammer rides on, and this would allow the hammer to go forward and fire the gun. A transfer bar is only in the way of the hammer when the gun is being fired. The hammer block is only in the way of the hammer when the gun is at rest. When the gun is cocked, either single or double action, the hammer block drops down out of the way. Sort of the opposite of a transfer bar. It should be in there for your safety. The reason it was incorporated into the firing mechanism, is that some guns WERE dropped on the hammer and DID fire as a result of shearing the pin the hammer pivots on.

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Louie the Lump
NRA Life