Gas Cutting Top Strap


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BruiseLee
August 28, 2012, 10:28 AM
Recently I was watching this youtube video on the Ruger LCR: http://www.youtube.com/watch?v=V0h3tz4pAF0

In it, there is some significant flame cutting of the top strap of the Ruger right above the forcing cone. It got me thinking about my revolvers. I pulled out my oldest, most shot, .357 Magnum revolver, an old S&W M66-1. There was a line of eroded metal going across the width of the top strap, but it wasn't very deep. Like most people, I've shot mainly .38 Spl. thru my K frame, but I'm sure I've shot a couple of thousand rounds of .357 mag out of it over the years.

Has anyone actually shot their revolver to the point where so much metal has been blasted off of their gun that it has become unsafe to fire? Has anyone done a military Glock like test with a S&W K frame to see how many rounds it can fire without any major malfunctions or part breakages?

Also, does everyone agree that the "melted aluminum" the video reviewer sees on the front of his LCR's cylinder is actually just lead deposited from the bullets he's fired?

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greyling22
August 28, 2012, 10:38 AM
back in the day I noticed some gas cutting on my revolver. I did some research and it seems to happen a bit to all revolvers, but only cuts in a little ways then stops. Shouldn't be a problem for you.

Sam1911
August 28, 2012, 10:42 AM
As greyling says, generally flame cutting just goes so far and then seems to stop.

There is no rash of flame-cut-in-two .357s. They may crack a forcing cone, develop too much endshake, even stretch the frame window, but the don't seem to suffer any actual harm from flame cutting.

Note that the scandium alloy frame guns are usually fitted with a stanless blast shield just above the gap, so apparantly S&W thinks it could be a problem with those.

Varmiter
August 28, 2012, 10:45 AM
I have heard......repeat.....HEARD that it is best NOT to clean that portion of the top strap. Let the crud build up. In the end, the crud somewhat protects the strap from further erosion.

YMMV

Chris

Guillermo
August 28, 2012, 11:32 AM
"flame cutting" is not what it sounds like.

it sounds like it is a torch which heats the metal and blows it away with expanding gas.

Such is not the case. The metal doesn't get near hot enough for near long enough to become molten.

It is more analogous to "sand blasting".

The unburned powder is abrasive but it can't maintain it's direction and velocity.

beaded powders seem to have more "sand blasting" power.

The effectiveness of the abrasive is limited so it stops, often, soon after it starts.

As to the LCR video, it is lead. If anyone took shop class they know that it takes a LOT of heat and some time to heat metal to the point that you can "blow it away". Even an aluminum beer can would not get hot enough to melt in the small amount of time it would be subjected to the heat.

CraigC
August 28, 2012, 12:03 PM
It is more analogous to "sand blasting".
Yep!

243winxb
August 28, 2012, 08:39 PM
"melted aluminum" is lead. Top straps do get cut, mostly with light for caliber bullets and maximum loadings. http://i338.photobucket.com/albums/n420/joe1944usa/Firearms%20%20and%20%20Reloading/SW329PD.jpg http://i338.photobucket.com/albums/n420/joe1944usa/Firearms%20%20and%20%20Reloading/SW325PD.jpg Your 66 should not have a problem.

rjrivero
August 28, 2012, 09:10 PM
243winxb, the top picture looks like the blast shield is missing?

rcmodel
August 28, 2012, 09:38 PM
It is missing.

Thats why the top strap is cut.

Must have made some true believers since this post.
http://www.thehighroad.org/showpost.php?p=7738487&postcount=12

rc

lobo9er
August 28, 2012, 09:50 PM
I have heard......repeat.....HEARD that it is best NOT to clean that portion of the top strap. Let the crud build up. In the end, the crud somewhat protects the strap from further erosion.

YMMV

Chris

That sounds like it could be an 'ol wives tail but it also sounds like it could be true! Hmm anyone no for sure or hear that also?

duck911
August 29, 2012, 12:37 AM
I have read that a cheap and easy solution is to cut a piece of straight razor into shape and epoxy it into place as a heat shield, on guns where a shield doesn't exist.

Protects the area and is easily enough replaceable.

I have not tried it as I don't have this issue with my revolvers currently, but seems like a reasonable work-around.

--Duck911

rcmodel
August 29, 2012, 01:40 AM
I think 35,000 PSI of white hot gas and powder granules would take the epoxied razer blade out the first shot.
And stick it where the sun don't shine in your otherwise unblemished body!!

I would not try it on a bet!!

rc

Warp
August 29, 2012, 04:04 AM
"flame cutting" is not what it sounds like.

it sounds like it is a torch which heats the metal and blows it away with expanding gas.

Such is not the case. The metal doesn't get near hot enough for near long enough to become molten.

It is more analogous to "sand blasting".

I had never heard that before...but a lightbulb just went off over my head when I read that.

Duh!

It was so obviously that somebody had to point it out to me. Thanks:cool:

1911Tuner
August 29, 2012, 06:57 AM
it sounds like it is a torch which heats the metal and blows it away with expanding gas.

Such is not the case. The metal doesn't get near hot enough for near long enough to become molten.

It is more analogous to "sand blasting".

True, but it's not necessary to actually melt the steel. All it has to do is anneal it a little to a micron's depth, making it more vulnerable to the sand-blast effect of the powder ash. Lather, rinse, repeat...and you start to see it cut into the steel.

And it does weaken the top strap. That part of the frame is subjected to some pretty high tensile stresses.

Guillermo
August 29, 2012, 11:26 AM
it's not necessary to actually melt the steel. All it has to do is anneal it a little to a micron's depth, making it more vulnerable to the sand-blast effect of the powder ash.

that makes sense

thank you

(I love THR)

Jim K
August 29, 2012, 12:37 PM
"it sounds like it is a torch which heats the metal and blows it away with expanding gas."

Well, it is. Hot gas erodes and burns steel without melting it because the heat doesn't last long enough to melt the metal. One Signor Bernoulli says that if you channel a moving fluid into a smaller space, it goes faster. That is why water comes out of a hose faster if the nozzle is smaller, why airplanes fly, and why we get throat erosion in barrels.

In this case, the constriction is between the barrel face and the forcing cone. It is worse with a smaller barrel-cylinder gap, one reason gun makers don't cut the gap down (another reason is cylinder lockup from heat expansion).

That constriction causes the hot gas to speed up, and that high speed is a major contributor to gas cutting. One way to reduce or eliminate gas cutting would be to angle off the rear top of the barrel, limiting the constriction and allowing the gas to escape. But that would weaken the forcing cone. Another is to increase the b-c gap to around .010". And of course, some type of shield can be used, or a plate of material like stellite inserted into the top strap, but that would weaken the top strap.

The statement that the gas cutting will go only so far is true. The metal of the top strap absorbs the heat of the gas, and cool gas won't flame cut.

Jim

BruiseLee
August 29, 2012, 06:33 PM
Actually, no one has mentioned a revolver that solved the gas cutting problem completely. Back in 1895, no less. I'm talking about the Nagant M1895 revolver. It had a unique gas sealing system. The gun's cylinder would actually move forward when you cock it, closing the gap between the front of the cylinder and the forcing cone. I think this system was good for an additional 50-150 fps in velocity.

http://farm4.static.flickr.com/3188/3012265166_171e0cd273.jpg

This system worked well enough to be used by the Red Army in WW2, and could actually be used with a silencer, I mean suppressor.

unspellable
August 29, 2012, 07:10 PM
Given a steel frame, it's my belief flame cutting is largely dependent on the load. The notorious example was the 357 Maximum. Its parent cartridge, the 357 SuperMag, was designed to push a heavy for caliber bullet. Ruger did not want to make the Blackhawk frame window long enough to accommodate the 357 SuperMag, hence the 357 Maximum which is shorter. The real problem was that Remington went for hyper velocity and cooked up a load using a big charge of slow ball powder behind what a 357 SuperMag shooter would call a light bullet. The Blackhawk had a serious erosion problem and became history. A problem those of us with 357 SuperMags using proper SuperMag loads never experienced.

PS Nominal cylinder gap on my 357 SuperMag is 0.003 inch.

paul105
August 29, 2012, 08:27 PM
ref 243winxb & rcmodel posts above:

This is what the blast shield looked like after 1,900 rounds -- I emailed the picture to S&W and asked if this was normal -- thier answer was yes:
.
.
http://i112.photobucket.com/albums/n172/Paul105_photo/blastshield.jpg
.
.
850 rounds later the blast shield eroded in half and fell off:
.
.
http://i112.photobucket.com/albums/n172/Paul105_photo/329-2-1.jpg
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resulting in the picture (post above by 243winxb) of the eroded top strap which had been "protected" by the blast shield. Picture emailed to S&W who emailed a prepaid label for return.
.
.
http://i112.photobucket.com/albums/n172/Paul105_photo/329-1-1.jpg
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There were no "light for caliber bullets" shot in the gun.

Paul
.
.

HKGuns
August 29, 2012, 09:01 PM
The examples above appear to be light alloy frames? Is this the case?

Does steel cut anywhere nearly as bad as these examples? Since I don't see a blast shield on my steel framed pistols I have to imagine this problem is not universal.

unspellable
August 29, 2012, 09:46 PM
Gas cutting occurs on all revolvers to some extant. Usually minor. Steel is much more resistant to this effect than aluminum or possibly titanium. However, even the aluminum frame revolvers usually only have a blast shield if they are chambered for the hotter loads.

Note that the so called "scandium" frame revolvers actually has an aluminum alloy frame. The scandium is added to the aluminum alloy in the range of 1 to 3% This does much to strengthen the aluminum alloy, but it's still really an aluminum alloy.

beag_nut
August 30, 2012, 06:59 PM
+1 for unspellable.

Drail
August 31, 2012, 10:21 AM
Aluminum is for airplanes and beer cans. For a revolver frame, no thank you. Apparently the "blast shield" wasn't such a great idea either.

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