Howdy
A couple of things.
First off, this is the only firearms forum where I have ever heard it stated that the old Hand Ejectors, made prior to the introduction of the current style of hammer block, introduced during WWII, should be only loaded with five rounds. That simply is not true.
Firearms manufacturers at the turn of the Century were acutely aware of the short comings of most of the old Single Action designs of the Nineteenth Century. Particularly the well deserved advice to never load one with a live round under the hammer.
Let's look at a few photos.
Here are the action parts to a Colt Single Action Army. Notice in particular how thin the upper tip of the trigger is. The tip of the trigger is called the sear, and it engages the various notches on the hammer to bring the hammer to the 'safety cock' position, half cock loading position, and full cock.
In this next photo, I have included a couple of arrows. One arrow points to the sear, the other to the so called 'safety cock' notch on the hammer.
Notice how there are overhanging lips on the 'safety cock' position and the half cock position. The purpose of those lips is to trap the sear, so the trigger cannot be pulled when the hammer is in those positions. The so called 'safety cock' position pulls the hammer back about 1/8" so the firing pin will not contact a primer. The problem is the cross sections of the metal at these spots is so thin that a good blow to the hammer will either shear off the over hang of the notch, or shear the sear right off the trigger. This has been documented many times, and it is the reason one should never carry an old fashioned single action revolver with a live round under the hammer. Dropping the gun from waist height so that the hammer spur strikes the ground is almost assured to shear off something and discharge the weapon. Accidentally dropping a saddle stirrup onto the hammer of a holstered gun can have the same effect. The same with the old Three Screw Rugers. That is why Ruger went to the transfer bar design in the 1970s.
Unfortunately the design of a SAA prevents me from assembling the parts in the frame so their true relationship can be seen, without drilling some holes in the frame.
So lets look at another classic single action revolver, with a side plate that can be removed to see the relationship of the parts.
This is a S&W 2nd Model Russian, made in 1875. The first photo shows the hammer all the way down as it would be after the revolver was fired. The sear can be seen resting against the hammer, ahead of the loading position notch.
The next photo shows the hammer back to the loading position. This position withdraws the firing pin from the immediate vicinity of the primers, and frees the cylinder to rotate for loading. The cross section of the parts here is slightly more robust than with the Colt, still I would not carry this revolver loaded with six rounds, a good blow to the hammer could still shear something off. I have seen plenty of old revolvers with broken off notches.
Just to get the idea, here the hammer is at full cock.
OK. Let's jump forward about 25 years or so. As I said earlier, manufacturers of quality firearms were well aware of these shortcomings with some of the older designs. As they began moving into producing double action revolvers, the mechanisms were radically different. And this provided opportunity for improvement. Iver Johnson had a well known publicity campaign called 'Hammer the Hammer' with illustrations of a hammer striking the hammer of their revolvers. The idea was the gun would be safe fully loaded, with a live round under the hammer.
Let's look at the Smith and Wesson Model 1899. This model employed a spring activated rebounding hammer.
In the first photo I am holding the trigger back with my finger. This is the position of the mechanism when the revolver discharges. Notice the hammer has come to a hard stop against the frame. Notice the piece directly below the hammer. It is actually two pieces, the Rebound Lever and the Trigger Lever. The trigger spring can be seen trying to rock these parts up, but my finger is holding them back, keeping the spring compressed.
In the second photo I have released the trigger. The trigger spring has rocked the pair of parts slightly clockwise. The Trigger Lever has pivoted the trigger forward. But notice how the hump on the top of the Rebound Lever has rocked the hammer slightly back, pulling the firing pin away from any primers. That is the rebounding hammer design of the Model 1899.
The problem with this design was it depended on the trigger spring to keep the hammer back. Push hard enough on the hammer and the spring will be compressed, allowing the firing pin to protrude through the frame and contact a primer.
That's probably why this model was only made for three years. I would probably be reluctant to carry a Model 1899 fully loaded.
Now, let's look at a modern Smith.
Little bit of a joke on my part, this 38 M&P Model of 1905 2nd Change left the factory in July of 1908. Look at the part underneath the hammer. That is the Rebound Slide. The Rebound Slide has been a part of every Smith and Wesson made from 1902 until today. And the rebound slide is why they are safe to load with six rounds.
Notice the hump on the top of the slide. There is a very strong coil spring compressed inside the Rebound Slide. The spring is bearing against a pin in the frame. The spring pushes the Rebound Slide forward, which in turn pushes the trigger forward. But more importantly, when the Rebound Spring slides forward, the hump on top wedges itself under the bottom of the hammer, forcing it to rotate counterclockwise a small amount. We are not talking about a spring holding the hammer back here, as was the case with the Model 1899. That is a solid block of steel sliding against a large bearing surface of the frame, preventing the hammer from rotating all the way forward. It would take a heck of a blow to the hammer to break anything here. About the only way it can fail is if the blow is so severe it breaks or bends the stud the hammer rotates on. And that would take a lot of force. I have a whole bunch of revolvers of this vintage, both 38s and 44s, and I do not hesitate to load them with 6 rounds. You don't really think all the thousands of policemen who carried these revolvers up until WWII were loading them with only 5 rounds, do you?
The shape of these parts has changed over time. This pair of photos of a 44 Hand Ejector 4th Model of 1950 shows the parts have changed a bit, but the function remains the same.
The wedging action of the Rebound Slide is clear here. The spring in the Rebound Slide has pushed the slide forward and the hump at the top of the Rebound Slide has forced the hammer to rotate back slightly, removing the firing pin from contact with any primers. Although a spring is required to push the Rebound Slide forward, it is the geometrical relationship of the mating parts that forces the hammer back.
At some point S&W introduced their first hammer block. It was unlike the WWII version, it was a piece of spring steel pressed into the side plate. A wedge on the hand (pawl) would shove the hammer block sideways out of the way of the hammer as the pawl rose. This one is from a 38/44 Heavy Duty that shipped in 1930.
This photo shows the relationship of the parts.
Personally, I have always felt that the hammer blocks in Smith and Wesson revolvers are mere redundancies. It is the Rebound Slide that really keeps the firing pin away from a live primer under the hammer. Yes, I have heard the stories about the sailor killed when a Victory Model struck the deck of a destroyer. I have never seen any documentation to that story. While the accounts of accidental discharges with old fashioned single action revolvers have been well documented.
For reference, here is a photo of that same 44 HE with its modern hammer block in place. It would take a heck of a blow to the hammer to shear off anything so that hammer block actually came into play. Much more of a blow than would cause an old Single Action to fire.
OK, time to get off the soap box.
S&W began heat treating cylinders at slightly different dates, depending on the model. On page 139 of the Third Edition of the Standard Catalog of Smith and Wesson it states that for the 38 M&P Model of 1905, 4th change, heat treating of cylinders started at about SN 316648, circa 1920. I might add that I have read the primary reason for heat treating cylinders at that time was not so much for strength, as it was to keep the bolt stop notches from being battered.
As for what is safe to shoot in these old revolvers, you can bet the police loads of their time were not light loads. I have not bought any 38 Sp factory ammo in years, but when I shoot my early 20th Century Smiths I do restrict them to mid-range loads.
And I do shoot them.
