Howdy Again
Regarding hammer blocks:
There have been three different styles of hammer blocks inside S&W revolvers over the years.
This is the lockwork of a Model 1917 that shipped in 1918. It has no hammer block. The lower arrow is pointing to the Rebound Slice, specifically the bump on the top of the rebound slide. When the trigger is pulled or the hammer cocked, the rebound slide moves backwards. There is a strong coil spring inside the rebound slide and when the trigger is released the rebound slide moves forward, shoving the trigger to the forward position. When this happens the bump on top of the rebound slide engages the bump on the bottom of the hammer, rocking the hammer back slightly. This pulls the firing pin away from the primer of a fired cartridge. This is necessary with a revolver with a cylinder that swings to the side. If the hammer was not withdrawn slightly, the firing pin would jam in the fired primer and the cylinder could not be opened for reloading. Notice the space between the top of the hammer and the angled portion of the frame where the hammer comes to rest when it falls. For some time, this arrangement was felt to be adequate. Revolvers like this were routinely carried fully loaded, relying on the rebounding features of the rebound slide and the hammer to keep the revolver safe.
At some point it was decided a hammer block should be added to the design. This is the first style of hammer block that was added to S&W revolvers. I do not have an exact date for when this style of hammer block was added, but it is inside a 38 M&P that shipped in 1920. The hammer block is a piece of spring steel peened to the side plate. It rests in a slot milled into the side plate. Difficult to see see in this photo, but at the top of the hammer block is a rectangular tab projecting towards us in this photo. The spring action for the hammer block normally keeps the rectangular tab at its top positioned between the hammer and the frame, in the space shown in the previous photo. My X-Ray camera was out for repairs when I took this photo so I cannot show the hammer block in position in relation to the hammer. I have placed the hand in the the recess in the side plate relative to how it would engage the hammer block. There is a pin running through a horizontal hole in the side plate. When the hand moves up, the pin wedges the hammer block down into its slot in the side plate. This pulls the rectangular tab back, freeing the hammer to fall all the way. When the trigger is released, the hand moves back down and the spring action of the hammer block makes it rise again to block the hammer.
This is the second, and more common style of S&W hammer block. I suspect in S&W's never ending quest to drive the cost out of manufacturing this style of hammer block was developed. It is just one piece. It is still made of spring steel, and operates similar to the older style. As with the earlier style, the spring action of the hammer block normally keeps it with the rectangle at the top positioned in the space between the top of the hammer and the frame, as can be seen in this photo. A ramp has been added to the side of the hand. There is a new tab on the side of the hammer block. When the hand rises it engages the tab on the side of the hammer block and forces the hammer block down into the slot in the side plate. Similar to the older style, this allows the hammer to fall all the way, firing a cartridge. When the trigger is released and the hand retracts, the spring action of the hammer block pushes it up again, positioning the top between the hammer and the frame again. At least that is the way it was supposed to work. There was an incident on ship board in 1944 during World War Two when a 38 revolver, probably a Victory Model, fell to the deck of a warship. The revolver landed on its hammer and it fired, killing a sailor. S&W had a large contract with the government at the time and the government instructed S&W to investigate what happened and to come up with a solution. Quickly. S&W set up some tests, and it was determined that the hammer block in the shipboard incident was probably coated with hardened cosmoline that prevented it from functioning properly. When the revolver struck the deck, the hammer block was in the wrong position. Perhaps the bottom of the hammer broke off, perhaps the rebound slide was crushed, it is hollow after all. Perhaps the stud the hammer rotates on broke. In any case the hammer block failed to do its job. S&W did some tests and determined that a 38 dropped on its hammer from waist high could indeed have a failure. The engineers were called in, and a new style of hammer block was designed and in production within a week. This particular revolver left the factory in 1939. Any of the early The 357 Magnum revolvers most likely had this style of hammer block inside.
This is the new hammer block that was designed in 1944. Not really, it is from a newer revolver, but this is what the new style looked like.. A stamped piece of sheet steel with a tab at the end twisted up 90 degrees.
This is how the new style of hammer block sits in a slot milled into the side plate. It is a relatively loose fit and the hammer block is free to move in its slot.
This is the position of the hammer block with the hammer at rest. The twisted tab at the top of the hammer block is positioned between the hammer and the frame. The bump at the top of the rebound slide is still doing its job of engaging a bump at the bottom of the hammer, withdrawing the hammer from the frame. A pin has been added to the side of the rebound slide. When the trigger is pulled or the hammer is cocked, rebound slide moves back as it always has. The pin in the rebound slide engages the slanted slot in the hammer block, drawing it down at an angle. This allows the hammer to fall all the way. When the trigger is released, the rebound slide moves forward as always, and the hammer block rises up to block the hammer again. This is the style of hammer block built into every S&W revolver since the 1944 shipboard incident. At that time, all the Victory Model revolvers with the older style hammer block were recalled and the new style was fitted to them. Victory models in production at that time had the new hammer blocks installed and the 'V' prefix of the serial numbers was changed to 'SV' to indicate the new style hammer block was inside.
It should be noted that all three styles of hammer blocks are/were 'redundant' safety devices. The rebound slide always was the first safety device, the hammer blocks only came into play if something failed, allowing the hammer to fall al the way forward. Notice in this photo there is a small amount of space between the hammer and the hammer block. The hammer never actually touches the hammer block unless something has failed. It has to be this way or the hammer would be pinching the hammer block and make it more difficult to withdraw.
Anyway, that is the style of hammer block that is still inside every S&W revolver manufactured to this day. Since 1944. So any revolver with a Model Number, instituted in 1957, such as a Model 27, will have this style of hammer block inside.*
*Unless some bozo has removed the hammer block thinking it will make the revolver a little bit slicker to shoot. Yes, it happens on occasion. If you peek into the area of the hammer with a strong light while slowly cocking the hammer you should be able to see the hammer block moving down out of the way.
