Hammer w/firing pin built in are generally not safe to carry with hammer resting on loaded chamber.
Howdy Again
As I said earlier, whether or not the firing pin is mounted on the hammer or in the frame, has nothing to do with whether or not a revolver is safe to carry with a live round under the hammer.
The S&W 44 Hand Ejector, 4th Model in the photo I posted in post #10 has the firing pin in the hammer, as does every S&W revolver made from 1899 on and up to very recently. Any S&W revolver made after 1944 is safe to carry fully loaded because it has the modern hammer block in it, whether or not the firing pin is mounted to the hammer or mounted in the frame.
The very earliest S&W Hand Ejectors, starting in 1896 were not safe to carry fully loaded, because despite the rebounding hammer, they had no hammer block inside. This is a photo of the interior of an early S&W 38 Military and Police revolver. This gun had the same basic rebounding hammer that S&W has put into all their revolvers since 1905. You can see the hump on top of the rebound slide has wedged the hammer back from the frame, withdrawing the firing pin from contact with the primer of a round under the hammer. At first it was thought this was safe enough. However, S&W later decided to add a hammer block as a redundant safety mechanism once it was discovered that a forceful blow to the hammer spur could cause the hammer to fracture where I drew the red line, causing the hammer to move forward forcefully, possibly firing a live round under the hammer.
This 38 M&P Target Model left the factory in 1917. It has the first type of hammer block that S&W installed in their revolvers. There is still a hump on top of the rebound slide, wedging the hammer back from the frame. The hammer block is a piece of spring steel pressed into a slot in the side plate. There is an ear on the hammer block projecting towards us in this view. Normally, the ear of the hammer block was positioned between the hammer and the frame, preventing the hammer from moving forward if the hammer spur was struck with a massive blow and something broke. There is a spring loaded pin in the side plate that activates the hammer block. An angled surface on the hand pushes the pin in whenever the hammer is cocked or the trigger is pulled. This withdraws the hammer block into the side plate, allowing the hammer to fall all the way. When the trigger is released and the hand moves down, the hammer block springs back into position blocking the hamemr.
This is the second type of hammer block S&W installed in their revolvers. This particular 38 M&P left the factory in 1939. The hammer block is still a piece of spring steel staked into the side plate, but there is no longer a spring loaded pin to activate it. Instead, a ramp on the hand pushes against a tab on the hammer block as the hand rises. This withdraws the hammer block into the side plate, in a manner similar to the earlier style of hammer block. This style of hammer block has less moving parts and was probably less expensive to produce than the first style.
In 1944 a sailor was killed when a 38 Victory Model with the second style of hammer block discharged when it fell to the deck of a warship. I have no information on how far the pistol fell before striking the deck, but this incident is well documented. The military ordered an investigation. The results were that as so often happens, the accident happened as a result of a cascade of events. It was determined that hardened grease inside the revolver most likely prevented the hammer block from springing back to the 'safe' position. And with the hammer block not functioning properly, when the hammer spur received a strong blow, something inside fractured, causing the fatal discharge. S&W was still supplying Victory Model revolvers to the military at this time. S&W was ordered to come up with a solution if they wanted to keep their lucrative contracts with the government. The engineering staff was called in and working night and day for one week they came up with the present design of hammer block, which has been installed in every S&W revolver ever since.
Single action revolvers are a completely different story.
This is a photo of the moving parts in a Colt Single Action Army. Although this one was made in the 1970s, the parts are basically the same as they were in 1873, and are basically the same in a revolver that leaves the Colt factory today. There are three notches on the hammer, the so called 'safety cock' notch, the half cock notch, and the full cock notch. The upper tip of the hammer is called the sear, the lower arrow is pointing to it. The sear pops into the various notches as the hammer is pulled back. The upper arrow is pointing to the 'safety cock' notch. Notice this notch and the half cock notch have a small lip projecting over the notches. This lip traps the sear so that the trigger cannot be pulled when the hammer is cocked to these respective positions. Notice how thin the sear is. This is the basic weakness of the Colt design. If the gun is fully loaded with six rounds, and it falls to the ground, and happens to land on the hammer, either the sear may fail or the 'safety cock' notch may fail, allowing the gun to discharge. The cross section of the parts is simply very thin and they are not very strong. This fact is well known to anyone familiar with these revolvers, and is why they are not safe to carry fully loaded with a live round under the hammer.
As a side note, single action revolvers based on the SAA design imported into this country from Europe are required by the Federal Government to have a second, redundant safety mechanism built into them to prevent a discharge if the gun falls to the ground. There are two styles of these redundant safety devices, one is built into the hammer and cannot be easily removed, the other is built into the cylinder pin and can very easily be replaced because it is a poor design. Uberti has come up with a third style of safety in their latest revolvers, but these have just recently hit the market. Colt is not required to have a redundant safety built into the Single Action Army.
This is the hammer from a Three Screw Ruger Blackhawk. Notice the firing pin is not mounted to the hammer. Notice too that the hammer has the same basic 'three notch' configuration as the hammer of the Colt. This style of Ruger suffered from the same weakness as the Colt, the sear or the 'safety notch' could shear if the gun fell onto its hammer.
As a result of several costly lawsuits, Ruger completely redesigned their line of single action revolvers in the early 1970s to include a transfer bar. Notice I said transfer bar, not hammer block. A transfer bar functions the opposite of a hammer block. A revolver equipped with a hammer block cannot fire unless the hammer block has moved from its normal 'safe' position. A revolver equipped with a transfer bar cannot fire unless the transfer bar is in position to transfer the blow of the hammer to the frame mounted firing pin.
This photo of a modern Ruger Vaquero shows the transfer bar in position to transfer the blow of the hammer to the frame mounted firing pin.
I would show photos of the lockwork of some other brands of single action revolvers from the 19th Century, to show how they too were unsafe to carry fully loaded, but this forum only alows six photos to be attached to any post.
Regardless, the presence or lack of a firing pin on the hammer has nothing to do with how safe a revolver is to carry fully loaded.
Also, even without the modern hammer block inside a S&W revolver, the design was still less 'accident prone' than the old single action revolvers. In redesigning the hammer block in 1944, S&W did extensive tests, dropping guns onto a hard surface, and determined that the internal parts could fracture. Based on this, some believe that a S&W from before 1944 should never be carried fully loaded. I tend to disagree with this somewhat. The S&W design was still more robust than the old Single Action designs. I would never dream of carrying a Single Action Army fully loaded. I do on occasion load up an old S&W fully, and countless police officers did so for generations.