Can I stop flame cutting?

[truckemup97]

I just did a thorough inspection on my 640-1. I'm starting to get some flame cutting on the right side of the top strap. Nothing major yet, but still there. I've shot 10 rounds of 125 gr. .357 Federal self defense ammo out of it, everything else has been 158 gr. .38 Special. All has been a factory load or a factory reload (Zero brand). I know there was no flame cutting when I bought it a couple of years ago.

Two questions. Am I doing something wrong that is causing this? And is there anything I can do to prevent further cutting?

Thanks for the help.

 

[truckemup97]

I just did a thorough inspection on my 640-1. I'm starting to get some flame cutting on the right side of the top strap. Nothing major yet, but still there. I've shot 10 rounds of 125 gr. .357 Federal self defense ammo out of it, everything else has been 158 gr. .38 Special. All has been a factory load or a factory reload (Zero brand). I know there was no flame cutting when I bought it a couple of years ago.

Two questions. Am I doing something wrong that is causing this? And is there anything I can do to prevent further cutting?

Thanks for the help.

 

[diamonback68]

Originally posted by truckemup97:
Two questions. Am I doing something wrong that is causing this? And is there anything I can do to prevent further cutting?

Nothing you can do about if you continue to shoot it and you are not doing anything wrong. But not to worry, it will reach a certain point and stop.

 

[310Pilot]

"I've shot 10 rounds of 125 gr. .357 Federal self defense ammo out of it"

There's the cause. The cure: don't fire any more 125 grain .357 ammo, stick to the 158 grain. The 125 grain .357 Mag loads, while having a good reputation for stopping, also cause flame-cutting almost immediately, primarily due to much higher volume and velocity of gases and burning powder escaping from the cylinder behind the lighter bullet. BTW, the 158 gr .357 loads also have a great reputation for stopping power, and were the de-facto standard for many, many years before the 125 grain loads came into use. It is also probable that your 640-1 has sights better regulated to the 158 grain loads, anyway.

 

[pownal55]

my personal experience with handloading the 357 and flame cutting led more to powder choice than bullet weight. powders like h110 and win296 led to severe flame cut in all bullet weights. i found 2400 to give good velocity with less damage.

 

[idaho]

Can someone explain to me what flame cutting is? Thanks!

-idaho

 

[Lionhound]

Idaho,

It's erosion of the bottom of topstrap above the forcing cone due to the byproducts of ignition.

 

[july1952]

Truck,
There is a thread called "FAQ" right at the very top of this section in the forum. Scroll down a few pages once you click on the link. I put this explanation in the FAQ a while back:

http://smith-wessonforum.com/eve/forums/a/tpc/f/530103904/m/875107028

 

[Snapping Twig]

W296/H110 are the culprits, but bullet length is a key factor too.

I use these slow burning powders exclusively for all my magnum loads and I use @ 4# a year doing so.

I bought a 586-1 in early Sept. and so far run @ 800 rounds of full on magnum through it, both 170g Keith and 160g Thompson GC. Absolutely no increase in the minimal gas cutting it had when I bought it. Perhaps some scientific instruments could detect an increase, but nothing visible to the Mk1 A 1 eyeball, even under great magnification.

Gas cutting is typically self limiting, but the limit appears to increase when a light (short) jacketed bullet is used in concert with these slow burning powders. A sandblasting if you will from yet unburned grains.

 

[Muzzlefire]

Originally posted by truckemup97:
And is there anything I can do to prevent further cutting?

Yes, the cure is to "armour" the top strap. Try the following: Take a razor blade, cut it down to a small rectangular piece (by metal scissors and file) until it fits perfectly to the top strap area to be protected and glue it in place with a industrial heavy-duty two-component glue like Araldite or somewhat equal. Instead of a razor blade, a thin feeler gauge is equally fine to start with.

 

[tomhenry]

Originally posted by idaho:
Can someone explain to me what flame cutting is? Thanks!

-idaho

Dunno where I got it, but here it is:

The 125 grain bullets driven to maximum velocities used large charges of relatively slow-burning powders. Handloaders know the powder types as WW296 and H-110, among others. The combination of slow ball-type powders and the short bearing surface of the 125 bullets allows prolonged gas cutting of the forcing cone and top strap area, accelerating erosion and wear.

Borescope studies of rifle, machine gun, and auto cannon chamber throats shows a lizzard-skin-like texture due to this gas cutting damage, called "brinelling". The results of brinelling are fine microcracks that weaken the surface of the steel, and further promote erosion. In machine guns and auto cannons, barrel life is measured in terms of "useable accuracy", and round counts that determine this are based on group sizes at engagement ranges.

In the K-frame magnums, the forcing cone dimensions combined with the barrel shank dimensions results in a relatively thin shank at the 6 o'clock position, where a machine cut is made to clear the crane. This is usually where the forcing cone cracks. The L and N frames use much beefier barrel shanks and do not have this cut. S&W intended the K frame magnums to be "carried much and fired seldom" service arms, designed to fire .38 Specials indefinitely, with light to moderate use of .357 Magnums. You notice that S&W has discontinued production of K frame .357 magnums, no doubt due to product liability issues and a couple generations of K frame magnum experience.

 

[Gunhacker]

Yep... In addition to the flame cutting aspect of the 125gr .357 mag personal defense or other "performance" ammo, another thing to be wary of is the erosion of the forcing cone and possible failure, as in cracking.

Since I don't have a J frame to check, does the underside of the barrel at the forcing cone have a flat (relief cut) machined into it to give the gas ring on the front of the cylinder room to swing under the barrel when the cylinder is closed?

As stated, K-Frames have that, and it makes that area thinner than the rest of the forcing cone.

From info I've read, the 125gr bullets accelerate much quicker than the heavier bullets and they really slam into the forcing cone after exiting the cylinder. The constant battering of forcing cones with that relief cut on the barrel underside increases the likelihood of it cracking.

It was one of the issues why the L frame came into being, with the slightly larger dimensions, the relief cut is unnecessary on the barrel.

You want a really gnarly self defense round without the need for high velocity ?

If you can or know someone that reloads, try a Speer 148 gr. hollow based wadcutter seated back wards with that big honking cavity pointing forward... talk about super sizing a hollow point.

That was a self defense loading that Skeeter Skelton mentioned often for sub guns... that soft lead wadcutter readily expands upon impact at relatively low velocities. I've tried them in a 2" and 4" pre model 10's, accurate to about 25 feet, past that I would start to get an occasional bullet tumbling when shot from the 2" bbl.

The one thing I did not like with them though is they were difficult (royal PIA) if you wanted to use a speed loader for reloads, imagine having to align all 6 "straight nosed" cartridges with the 6 chamber openings in order for them to all slide in... using one of those "speed strips" was a lot faster.

 

[Whiskey Foxtrot]

Originally posted by truckemup97:
I just did a thorough inspection on my 640-1. I'm starting to get some flame cutting on the right side of the top strap. Nothing major yet, but still there. I've shot 10 rounds of 125 gr. .357 Federal self defense ammo out of it, everything else has been 158 gr. .38 Special. All has been a factory load or a factory reload (Zero brand). I know there was no flame cutting when I bought it a couple of years ago.

Two questions. Am I doing something wrong that is causing this? And is there anything I can do to prevent further cutting?

Thanks for the help.

I've got a friends' 386 PD in my safe. It has what looks like a stainless steel flame shield above the forcing cone.

Did S&W use these on J frames? If so, why not see about ordering one and install it yourself. Interestingly enough my 442-2 doesn't have one on it.

Bill

 

[cmj8591]

Don't worry about it. Keep shooting the 125's if you want. The flame cutting will get to a point and stop. It is cosmetic only and has no effect on the operation of the gun.

The only thing that concernes me is that you said you are only getting it on the right side of the frame. You might want to check the barrel/cylinder gap to make sure that the throat of the barrel is square. If it is then don't worry about the flam cutting.

 

[Lenshappy]

We just use some tin foil on the top strap to stop that crap... Juice Fruit works...

 

[Peter M. Eick]

Here is flame cutting on my 357 maximum.

 

[sar4937]

I measured up my M327 blast shield and it looks like it may fit several of my S&W's. It is a stainless steel shield that press fits above the forcing cone. A sacrificial shield.