Over-Torqued Barrel

[RedBerens]

I've heard that over-torquing the barrel on an airweight revolver can lead to frame cracking. Is there any way to tell if the barrel is over-torqued? Would the front sight lean to one side or another on these?

 

[RedBerens]

I've heard that over-torquing the barrel on an airweight revolver can lead to frame cracking. Is there any way to tell if the barrel is over-torqued? Would the front sight lean to one side or another on these?

 

[Erich]

It didn't on my dear, departed 38-2.

I learned it was overtorqued when the frame cracked.

I now use steel-framed revolvers.

 

[arfmel]

steel is our friend.

 

[MaineProbation]

There are a couple of things going on here. First of all, because of the elasticity of the aluminum frame and the steel barrel, an overtorqued barrel puts a heavy and constant load on the external threads of the barrel and the internal threads of the frame. This is in and of itself not a problem. The two machine elements, barrel and frame, are in an equilibrium situation. When you fire the revolver, however, other forces come into play. Due to internal pressure of the gas behind the bullet, the barrel instantaneously expands both lengthwise and in outside diameter, especially at the portion which is threaded and tightly fitting within the frame. Now if the frame is already stressed to near the elastic limit, gradually microscopic cracks may begin to form at the barrel/frame interface. These, once started, are prone to increase every time the piece is fired. Eventually, a macro crack forms at a point of maximum stress and the frame fails.

The barrel also expands due to heat of firing, and this is not instantaneous but continues as more rounds are fired. Now the heat transfer from the barrel to the frame also causes the frame to expand. Aluminum expands with heat at roughly twice the rate of steel so this, in theory, should relieve the stress at the barrel/frame interface somewhat. However, if the barrel is tightly torqued in the frame, there is a pulling back and forth at the threads as the barrel and frame expand at different rates with the heat of firing. This is something that does not happen with a steel barrel threaded into a steel frame, as both elements expand with heat at about the same rate.

Sorry, I'm not trying to be a know it all. I was originally trained as an engineer and do understand some of the failure mechanisms both in firearms and other machinery.

 

[MaineProbation]

After this boring dissertation, to answer your question, the only really good was to tell if the barrel is overtorqued is to use the Magnaflux (tm) or some other micro-crack detecting system to determine if micro-cracks are beginning to form. Chances are that, if the barrel is seriously overtorqued, these cracks will begin to form well before actual frame failure occurs.

 

[dfariswheel]

One symptom of a POSSIBLY (note "possibly") over-torqued barrel is a pressure "dimpled" or constricted bore.

When S&W first went to the non-pinned, torqued-in barrels, they had a problem with staff installing the barrels TOO tight.
This actually compressed the rear of the barrel in the threaded area, and caused the bore to have a "tight spot" in the rear.

This can be detected by running a tight patch down the bore.
If, near the rear of the barrel, you notice the patch gets suddenly tighter and harder to push, you "May" (note "may") have an over-torqued bore.

This is NO guarantee the frame was over-torqued, or that you have something to worry about.
Short of Magnafluxing the frame, all you need to do is watch for cracks in the frame.

The number of cracked frames S&W sees is really very small, and is usually on revolvers some clown has been shooting really hot loads through.

 

[Ben Dare]

What about those airweights that are found to have a cracked frame while still in the box unfired?

 

[anachronism]

Originally posted by dfariswheel:
One symptom of a POSSIBLY (note "possibly") over-torqued barrel is a pressure "dimpled" or constricted bore.

When S&W first went to the non-pinned, torqued-in barrels, they had a problem with staff installing the barrels TOO tight.
This actually compressed the rear of the barrel in the threaded area, and caused the bore to have a "tight spot" in the rear.

I had a 686+ like this. The revolver didn't shoot well at all. I checked the cylinder alignment with a range rod & couldn't get the rod past the frame juncture line. S&W rebarreled it. You guys are saving me a fortune here, I almost sold a 640-1 to buy an Airweight. Maybe I'll hold off until I see how this issue comes out.

 

[photoman]

I think it's important to remember that a cracked frame inder the forcing cone is not a catastrophic failure. That is, if I have to use my trusty 642 to defend my life, and it cracks on the first shot, I'm confident it'll get the other four shots off just fine.

 

[MaineProbation]

Photoman44 is correct. These Airweights (tm) seem to all exhibit the same failure mode: Lengthwise cracking of the frame in the threaded area under the forcing cone. Usually not a dangerous condition for the shooter. In fact, once the stress is relieved by the opening of the crack, one could possibly continue to use the revolver for years. I would even submit that some of these cracks have not even been noticed by the shooters. In some instances, the revolver could actually end up being MORE accurate because stresses in the barrel/frame interface are no longer present and you actually have what is called in rifle shooting a "floating barrel."