So Called K-Frame Flaw 125 gr 357 Magnum

[Minorcan]

I’m trying to learn from some one smarter than me. What is the story here. I keep hearing stories of “the K-Frame Flaw”. I shoot 357 Magnum ammo all the time. usually 158 gr but sometimes 125 gr. Does shooting lower grain weight ammo hurt the K-Frame S&Ws? If so how and why.

 

[Babysitr]

This subject is beat to death, after I got my M19. started shooting .38 spl just cause its fun. shooting limited amounts of .357 likely wont hurt the gun. look at your forcing cone and compare it to a model28 you'll see the difference! I don't shoot 125 gr. because I don't feel the need to. as a carry gun 125's are probably the deal. a friend of mine did crack his back in the day, gunsmith replaced barrel. said he shot tons of hot handloads. 158's easier on your gun, .38's easier yet. IMHO hope I'm right

 

[Protocall_Design]

The lower the bullet weight, the faster velocity it can be pushed. This is true for any caliber of gun. The most pressure is generated in the chamber and hits the forcing cone pretty hard on magnum loads.

The bottom of the forcing cone on a K frame has a flat milled on it to clear the top of the crane. That makes a thinner place on the barrel than the rest of it, so it's the first place to crack when it is over stressed.

I have seen a lot of K frame forcing cones cracked from shooting hot loads or just a lot of target loads. I had a M19 (before there were L frames) that was my only match gun for 3 years. I put around 30,000 rounds of wadcutters and a couple thousand rounds of magnums through it a year. It never did crack. I've had PPC guns that the barrel cracked after only a few tens of thousands of wadcutters. Once the forcing cone cracks, all you can do is replace the barrel. It won't shoot groups any more. Sometimes it binds up the opening and closing of the cylinder.

I have come to the conclusion that there is no way to predict if a barrel will crack, some do, some don't. I have long since switched over to L and N frames for competition. They never have that problem.

 

[Old_Cop]

I don't recall ever seeing any official announcement from S&W, but cracking the flat of the barrel and or flame cutting the top strap of model 19s have been given for the creation of the L frames.

 

[bigggbbruce]

It's not so called...

when you've cracked one.

 

[lrrifleman]

As I understand the issue, the 125gr bullets require more powder than heavier bullets ... generating more hear and flame at the barrel/cylinder gap, which allows the flame to cut the top strap.

 

[bigggbbruce]

As I understand the issue,

It's more about the forcing cone cracking.

 

[Donald Paul]

... hi everybody. Why do most folks refer to these anomalies as
cracks. These are actually FLAME CUTS caused by a very hot flame under extreme pressure {Think oxyacetylene torch, under very, very high pressure}. It will begin wherever gas leakage is
most likely, say at the forcing cone. {The top strap will suffer too}.
Once these hot gasses can find a way out, the leak will only grow and get worse. The 'K' frame is most at fault because of the thinner forcing cone at the six-o-clock location.
The lighter the projectile. the hotter the flame is behind the projectile. A heavier projectile uses up more of the flame prior to reaching the cylinder gap.
-Don

 

[JH1951]

... hi everybody. Why do most folks refer to these anomalies as
cracks. These are actually FLAME CUTS caused by a very hot flame under extreme pressure {Think oxyacetylene torch, under very, very high pressure}. It will begin wherever gas leakage is
most likely, say at the forcing cone. {The top strap will suffer too}.
Once these hot gasses can find a way out, the leak will only grow and get worse. The 'K' frame is most at fault because of the thinner forcing cone at the six-o-clock location.
The lighter the projectile. the hotter the flame is behind the projectile. A heavier projectile uses up more of the flame prior to reaching the cylinder gap.
-Don

So, what you are telling me is that what you have pictured is a flame/gas cut, not a crack? Perhaps I have been misinformed for years?
Anyone willing to lend comment to straighten me out?

 

[Minorcan]

Thanks for the explanations. I have shot many rounds of 357 Magnums and I know some 125 gr ammo. Never had any issues, in my Model 19, 28 or newer 60s. Maybe I’m just lucky. The picture does look like a blowout/burn more than a crack or maybe a crack that allowed hot gases to open it up. I’ll keep an eye out though and be more selective on magnum ammo.

 

[Donald Paul]

So, what you are telling me is that what you have pictured is a flame/gas cut, not a crack? Perhaps I have been misinformed for years?
Anyone willing to lend comment to straighten me out?

... yes JH, it's a cut made by a hot, hi-pressure gas. The same gas that can cause serious damage to your hand if you get your hand or any other part of your body next to and close to the cylinder gap.
This problem was well known to a shooter of a revolving rifle of the old days. The arm between the wrist and elbow had to wear protection to shield the shooter's arm. A very severe blast is emitted from that cylinder gap in a 360 degree arc.

 

[stansdds]

Plenty has been written about the potential for the forcing cone in the 19/66 to crack. Hot loads, especially with bullets lighter than 140 grains, will accelerate erosion of that thin throat. The bottom of the throat is the thinnest part and the area where a crack is most likely to form. Best advice for the old 19/66 is to shoot magnum loads sparingly, especially with the lightweight bullets.

S&W N-frame revolvers have thick forcing cones and are more durable. The L-frame was developed as a compromise, slightly bigger than the K-frame, allowing a full thickness forcing cone, but smaller than the N-frame.

S&W is introducing a redesigned Model 19. The blueing is their new process, I've heard it is sensitive to cleaning solvents. It does have the safety lock, which I personally do not like. But it has the two-piece barrel system that eliminates the thin forcing cone and the crane lock, so it may well take more abuse from hot loads and lightweight bullets.

 

[bigggbbruce]

... hi everybody. Why do most folks refer to these anomalies as
cracks.

Because when my 66 cracked, it then deformed the forcing cone and the cylinder would not open because it bound up on the broken portion of the barrel. It showed little to no erosion.

The picture shows a crack that was then burned open after prolonged use after it cracked.

 

[BAM-BAM]

Questions....I'm not a metallurgist.........

I have seen/observed the flame cutting on the top strap of the frame at the cylinder gap.. the cutting seems to stop with just a fine line... but have not seen the same in the forcing cone....

always "heard/reported" that the "crack" was a catastrophic failure not a slow cutting process.

If it's a cutting why don't we see it in all forcing cones? J-N frame!

 

[bigggbbruce]

always "heard/reported" that the "crack" was a catastrophic failure not a slow cutting process.

One day fine.. next day cylinder bound up on barrel.

I have a feeling that some out there if you look real close with good magnification you will see the problem on your beloved K frame magnum.

 

[cowboy4evr]

I have read that the 125 gr bullet loaded in the K-frame used as much as 21.0 grs of W296/H110 . That's almost the same charge load for full magnum loads in the 41 magnum and that's in an " N " frame .
Over time it just literally beat the K-frames to death . They usually needed a trip back to the factory to " tighten " them up . The forcing cone issue is one of very limited actual cases, but it did happen .
I researched it , a lot and found the statement that smith / Wesson issued saying to only use what the gun was designed for , 158 gr. or heavier bullets . S&W over the years had received so much flack from shooters because they could not load the Elmer Keith 173 swc in a 357 magnum case and crimp in the crimp groove in the " N " frames . So the factory designed the K-frames with the longer cylinder to accommodate the " Keith " swc .
Smith / Wesson later issued the statement to only shoot limited 357 magnum loads in 19's/66's . This was because police debt's continued to use the light weight ( 110-125) gr bullets because of so much " heat " they received about over penetration .
I have several 19's , today I do not " stoke " them to the max 357 magnum load . I have L and N frame 357's for that . I really like 13.5 grs of Alliant 2400 using a 158-173 gr cast swc in my K frame 357's as a max load . Regards, Paul

 

[Alk8944]

It is not a "flaw" in the Combat Magnum/Model 19 revolver, it is an incompatibility between a revolver design dating to 1899 and a cartridge operating at 8,000-12,000 PSI, and the high-intensity variations of .357 Magnum operating at three times the original pressure the gun was designed for!

There is a slightly thin area at the bottom of the barrel shank to clear the yoke and gas ring of the cylinder. At original pressures, even +P .38 Special, and standard bullet weight .357 Magnum pressures the design was adequate. When the lighter 110 and 125 grain bullet loads became popular because of the higher velocity they generated this thin area of the barrel shank often would fail. Not so much as pressure as the dynamics of the load imposing significantly higher strain on the barrel shank. So far as I know there has never been an actual engineering study to determine the specific reason for the failures, but there is more than adequate anecdotal evidence proving that these failures do happen, sometimes. You have to understand that 110 and 125 grain jacketed .357 magnum factory ammunition did not exist when the Model 19 was originally designed, and very little jacketed 158 grain ammunition. As long as lead bullet ammunition was used there were no reports I have ever heard of barrel failure!

I have heard reports of the failure immediately causing functional problems, and have seen revolvers with cracks still functioning normally and the owner was unaware they had a cracked barrel. It does seem these are sudden, catastrophic failures as a result of progressive fatigue.

You have to remember the Combat Magnum/Model 19 was never intended for full-time use with full power .357 Magnum ammunition. The intent was a lighter weight police service revolver ala the Combat Masterpiece/Model 15, to be shot mostly with .38 Special ammunition that the design was originally intended for, but capable of safely firing full power .357 Magnum ammunition of the day when needed by law enforcement for the improved performance. The problems occurred when people started using the guns as full-time .357 Magnums and with ammunition that didn't even exist when the model was originally proposed and designed.

 

[RichCapeCod]

A very long time ago, when I was serving in the NYPD ’s Firearms & Tactics Section (as a Sgt., and later as a Lt., I ran the Police Firearms Instructors School, Heavy Weapons Training and Research and Testing) I visited the Remington factory in, I believe, Connecticut.

Speaking with one of their engineers, he stated that .38/.357 wear on revolvers was less intense with projectile weights from 140 through 158 grains. He stated this was due to these rounds less abrupt “time-pressure” curves.

I’m not an engineer but have followed his advice ever since.

Rich

 

[Texas Star]

I once published an entire article on this,but will say here just that no one has mentioned that burning grains of powder (ejecta) that escape from the ctg. case in light bullet ammo, but which are burned by the heavier bullets being slower to leave the case. This ejecta impacts the barrel breech/cone and erodes it. Also, heavier doses of powder were used, usually ball powders that erode cones more.

You can minimize the problem by not letting lead residue build up in the cone. That increases pressure.

I was told by S&W that Plus P Plus .38 ammo loaded for police depts. actually is as erosive as 125 grain .357 loads!

The sole purpose of such ammo was to let police tell reporters that they used .38 ammo, for PC reasons. But the pressure curve of much Plus P Plus ammo is severe.

I talked not just with S&W, but with several ammo companies, speaking with both PR people and engineers not normally available to the public. (I was an accredited gun writer.)

The overall feeling is that hot 125 grain and lighter .357 ammo is NOT recommended for K-frame .357's. If I fire that at all, it's in my Ruger GP-100.

I've seen a few photos taken of GP's fired extensively by handloaders who fired many rounds of that hot ammo. Even a GP can crack a barrel throat, if it's abused enough!

Don't worry about 125 grain .38 ammo: it isn't loaded hot enough to be an issue.

 

[Doug.38PR]

From what I've read and discussed over the years:

In a nutshell: Isn't the context of this really a problem only when we are talking about tens of thousands of 125 gr magnums being put through a gun (on a police range that has ammo budgets that far exceed what we are able to afford to shoot) that the owner fails to clean barrel/force the cone on a regular basis?

This can happen even to Colt Pythons (I frame) or 686 (L frame) (with those two lasting a little longer on wear) to my understanding if you put it in the above context.