What's gas cutting?

Oh yeah, let's get the usual references to Taco Bell and such out of the way early. I'm talking about the revolver kind of gas cutting, not the chili contest kind.
 
"Gas cutting" or "flame cutting" of the topstrap is where high-pressure gasses from the barrel/cylinder gap erode the topstrap of the revolver. The guns that brought this phenomenon to most folks' attention were Ruger's Blackhawks in .357 Maximum.
 
In a revolver, it's erosion under the topstrap at the gap between the cylinder and the forcing cone. Often found in old revolvers. I believe that severe and premature gas cutting in that area was the cause for discontinuing some of the revolvers chambered for .357 Maximum several years back.
 
At the forcing cone it is called erosion. The edges of the forcing cone become rounded and rough.
 
I have heard

that some folks don't clean the area of the top strap above the gap between cylinder and barrel. The theory is that the lead and carbon protect the metal underneath from erosion.

Any takers?

Ledbetter
 
Gas cutting happens any time super hot gas is forced through a small aperture. A fellow named Bernouli says that the gas speeds up under those circumstances and it ends up acting like a cutting torch. This happens not only on top straps, where the barrel-cylinder gap acts as the small opening, but in the corners of barrel grooves where the a jacketed bullet is not under enough pressure to expand and seal the groove fully. .45 autos firing hard ball are notorious for gas cutting of that type.

Erosion is also a form of gas cutting, caused in part when gas escapes around the bullet (the small opening again) before the bullet can move forward and seal the bore.

FWIW, S&W used to dish out their topstraps to prevent that kind of gas cutting, but it was too costly and they now say that the cutting is self-stopping, and cannot procede far enough (at least with factory equivalent ammo) to weaken the top strap.

Jim
 
I was going to mention the theory that gas cutting is self limiting, but Jim beat me to it.

The problem with the .357 Maximum was the fact that people were trying to launch light bullets at incredible velocities instead of boosting the velocity of heavy bullets to that of a typical 158 grain .357 Mag. Yes, I want Ruger to resume manufacture of the .357 Max. They now command premium prices since their frames are used in conversions for the .475 Linebaugh.
 
One way to extend the life of your S&W revolver is to take a carpenter's or artist's pencil (the ones with soft, rectangular shaped leads), and rub it on the topstrap immediately above the bbl. This is because of the phenomenon of top strap cutting. It used to be thought that this was due to the hot gas escaping from the bbl. / cyl. gap, but it has been shown that the problem was actually unburned powder grains in the gas acting almost as a sandblaster does. The graphite/polymer layer deposited by the pencil will effectively counter this phenomenon.
Click to expand...
The late Dr. Walt Welch supplied this bit of information about gas cutting.
 
My friend's S&W scandium frame .357 has a deflector above the forcing cone to prevent gas cutting of the topstrap. BUT it deflects unburnt powder back into our faces. Any ideas? I believe he sent it back to S&W but I have not heard results yet.
 
My little 38 diamondback has a gas cut topstrap. Not to deep, but pretty noticeable. It has taken over 20 years to get that way though.

I think gas cutting may be a function of the total volume powder burned in the gun. A 357 maximum just burns it faster then a 38 special.
 
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