Do Brass Frames Stretch?
Steve Sheldon
2019
One of the common things you will hear about brass-framed revolvers is that the frame will "stretch" if you shoot heavy loads in it. Like many myths, this one has a kernel of truth to it. People have noticed after shooting heavy loads with a black powder revolver that there is an increase in the gap between the cylinder face and the barrel. They assume that because there is an increased gap there, that the frame must have stretched.
It is unlikely that the frame has actually stretched. Black powder revolver loads for 45 Long Colt max out at around 15,000 PSI, and are typically much lower. The yield strength of brass is over 19,000 PSI. More importantly, you can see this "stretching" in Colt-style brass frames, and with Colts the steel arbor bears all the load, and it is for certain the steel arbor is not stretching, and if it did you would see it in steel-framed Colts as well. It's possible for the arbor to work loose in the brass frame, but if this were the case you would have a loose arbor and would know this right away.
What actually does happen is that the frame gets hammered by the cylinder.
On a black powder revolver, the steel cylinder is free to slide forwards and backwards along the arbor. As it slides forward, it is stopped when it hits the barrel face, and as it slides backwards, it is stopped by the frame of the revolver. In addition, when a black powder revolver is cocked, the hand pushes the cylinder forward slightly, creating a slight gap at the rear of the cylinder between the cylinder and the frame.
You can confirm this yourself with any black powder revolver. Make sure it's unloaded, and then hold it up to a light, looking at the side of the revolver. Notice there is a hairline crack of light you can see between the front of the cylinder and the barrel, and between the rear of the cylinder and the frame. Wiggle the cylinder back and forth with your fingers. Push it all the way against the frame and then cock the revolver. See how there is now a bigger gap between the rear of the cylinder and the frame?
When the revolver is fired, the recoil of the shot acts directly and immediately against the cylinder. The cylinder then rockets backwards along the arbor until it strikes the frame. Since brass is more malleable (softer) than steel, under heavy loads the brass frame will be dented by the cylinder. This is called "peening", as when you peen a rivet head.
2019
One of the common things you will hear about brass-framed revolvers is that the frame will "stretch" if you shoot heavy loads in it. Like many myths, this one has a kernel of truth to it. People have noticed after shooting heavy loads with a black powder revolver that there is an increase in the gap between the cylinder face and the barrel. They assume that because there is an increased gap there, that the frame must have stretched.
It is unlikely that the frame has actually stretched. Black powder revolver loads for 45 Long Colt max out at around 15,000 PSI, and are typically much lower. The yield strength of brass is over 19,000 PSI. More importantly, you can see this "stretching" in Colt-style brass frames, and with Colts the steel arbor bears all the load, and it is for certain the steel arbor is not stretching, and if it did you would see it in steel-framed Colts as well. It's possible for the arbor to work loose in the brass frame, but if this were the case you would have a loose arbor and would know this right away.
What actually does happen is that the frame gets hammered by the cylinder.
On a black powder revolver, the steel cylinder is free to slide forwards and backwards along the arbor. As it slides forward, it is stopped when it hits the barrel face, and as it slides backwards, it is stopped by the frame of the revolver. In addition, when a black powder revolver is cocked, the hand pushes the cylinder forward slightly, creating a slight gap at the rear of the cylinder between the cylinder and the frame.
You can confirm this yourself with any black powder revolver. Make sure it's unloaded, and then hold it up to a light, looking at the side of the revolver. Notice there is a hairline crack of light you can see between the front of the cylinder and the barrel, and between the rear of the cylinder and the frame. Wiggle the cylinder back and forth with your fingers. Push it all the way against the frame and then cock the revolver. See how there is now a bigger gap between the rear of the cylinder and the frame?
When the revolver is fired, the recoil of the shot acts directly and immediately against the cylinder. The cylinder then rockets backwards along the arbor until it strikes the frame. Since brass is more malleable (softer) than steel, under heavy loads the brass frame will be dented by the cylinder. This is called "peening", as when you peen a rivet head.
You can see the effect of this peening in the above photo. Very clearly the back of the cylinder has left clear indentations in the frame race.
Once the frame has been dented like this, the cylinder now can move backwards farther than it originally could. When you look at the revolver, you will be able to see there is now an increased gap between the front of the cylinder and the face of the barrel. This is not because the frame has stretched - it is simply because the cylinder now can slide farther back along the arbor until it settles into the dents it has made in the frame face.
An increased gap between the cylinder and the barrel is bad for a few reasons. First, the increased flow of hot gasses escaping at this gap will increase the gas cutting action on the arbor and possibly other parts of the gun as well. In addition, since you are losing some of the energy of the charge you may see reduced velocities. It's also possible to see a reduction in accuracy.
So, heavy loads are bad for brass-framed revolvers, but not because the frame stretches. It's because the frame is being dented by the cylinder hammering into it under recoil.
Once the frame has been dented like this, the cylinder now can move backwards farther than it originally could. When you look at the revolver, you will be able to see there is now an increased gap between the front of the cylinder and the face of the barrel. This is not because the frame has stretched - it is simply because the cylinder now can slide farther back along the arbor until it settles into the dents it has made in the frame face.
An increased gap between the cylinder and the barrel is bad for a few reasons. First, the increased flow of hot gasses escaping at this gap will increase the gas cutting action on the arbor and possibly other parts of the gun as well. In addition, since you are losing some of the energy of the charge you may see reduced velocities. It's also possible to see a reduction in accuracy.
So, heavy loads are bad for brass-framed revolvers, but not because the frame stretches. It's because the frame is being dented by the cylinder hammering into it under recoil.