I've noted lots of postings regarding cracked forcing cones being the result of firing hot loads with short light bullets. However, I've not seen any analysis or explanation of why that occurs, only vague mentions about how the short bullets didn't seal the gap between the cylinder and the end of the barrel. Can someone come up with a more scientific explanation of this phenomena?

Yes, the real problem is that grinding a flat on the bottom of the barrel extension in K frame revolvers left a thin area too weak to always sustain the impact, pressure, and vibrational forces associated with shooting bullets at max .357 speed.
The bullet hits the forcing cone like hitting it with a hammer, and the faster it goes under higher pressure, the greater the impact shock. Light bullets under higher pressure strike the forcing cone faster.

The same load in the L frame produces the same force, but with more metal in the frame and barrel at the forcing cone, the shock is absorbed and dissipated without structural failure.

In engineering terms, the stress of firing should be no more than the ability of the material to accept the strain without material failure. And some safety factor is always good.

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Science plus Art

Would this imply that a modern Model 60 might be able to stand full 357 mag loads better than it's big brother K frames.

I don't believe the J frame magnums have a flat on the bottom of the forcing cone.

This is true. Your hand will give out before the Model 60.

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Science plus Art

Ken4, don't worry yourself about a cracked forcing cone on your 66. The cracked forcing cones were the result of firing countless hot 125 grain loads over a long period of time. This occurred primarily with LE agencies and was observed on a small percentage of the weapons. The issue has been a bit exaggerated over the years producing unwarranted fears. I have both a 66 and a 19 which I have shot a fair amount of 125 grain ammo through without issue. I shoot mostly 158 grain bullets in .357 and any load I choose in standard and +P .38 SPL loads. If you use a bit of caution, you will have years of trouble free shooting with your K-frame .357.
K-Frame 66 and 19s are scarce around my area and are snapped up quickly when the appear at a LGS.
They are my favorite S&W and I am on the watch for another one myself.

Two issues make for this issue.

1.) Recoil impulse. The gun rocks upward while the bullet continues straight.

2.) Gas plasma.

In the case of the short (125g) bullet, it leaves the cylinder before it completely engages the forcing cone. This allows an unguided moment and the result is impact with the bottom of the forcing cone.

The short bullet also allows a pass-by of the gas plasma which is harmful to the forcing cone. Longer bullets allow a more complete burn before the bullet exits the cylinder.

Combine these issues and you can cause damage over time.

So, full power loads with bigger bullets eliminates the issues.

Hope this helps.

I have also read that the few k frames that did crack had badly leaded forcing cones. lead build up will cause higher pressure, combined with hot rod 357s you have a perfect storm for cracking a cone. Keep your guns clean and loads normal and you will never have a problem. The whole K frame weakness rumor evolved into fact so that pawnshops could scam people out of a lot of money.

Don't be, you purchased a very solid, very usable firearm. You need to avoid only one thing, full magnum loads with bullet weights under 140 grains. You can shoot full power loads with heavier bullets all day and not harm your M66.

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"Sacramento" Bruce Conklin

The Lewis Lead Removers are great! Anyone that has a revolver should have a Lewis tool. I wouldn't worry about shooting 130gr from a 38sp. If they are factory 38s the pressure and velocity will be low enough to not be an issue. Just clean the gun before going back to 357mags, but that goes for any 357 not just the K frames.

I've yet to read of, or see actual proof of, a M-66 cracking at the FC. There may be pics around now, I don't know, but only a couple years back here there were several threads going about this subject and no one could come up with a pic of a 66 with a cracked cone. It was always M-19's with the issue. Many claim that the properties of the SS alloy used in the M-66 prevent the cracking issue.

As far as the M-60's go- S&W has come a long way in theri heat treating capabilities over the years, which is a big reason an M-60 from the last 10-15 years can withstand full power 357 ammo, while the same diameter cylinder from a 70's/80's gun couldn't. The same thing goes for the forcing cone area on the 60.

I avidly read as much from well respected gunsmiths as I can find online.
When cracked cones DO occur, it seems to be from badly out of time revolvers.
Having the bullet hit way off center will sometimes do it.

Another take of the subject: I have seen much wailing about
the thin forcing cones on the 696. I have yet to actually see one.
It certainly has not prevented this gun from selling for many times
it's original price (when you can find one).

JMHO YMMV etc

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Nemo

Interesting observation.

Having both K frame 357's and a 696, I can say this...

696's have had issues, but most use them wisely these days and do not make magnums out of them. Additionally, the forcing cone is concentric with no flat spot in exactly the wrong place, like a K frame.

I have never experienced a forcing cone failure, but I have searched for information over the years and what I posted earlier is my understanding of how it happens, based on sources I personally trust. Timing does not come into play overtly, but I suppose it's not helpful in any event.

Hope this helps.

IMO too many non scientists have come up with explanations that are both too complicated and probably wrong. So, go back to basic High School Physics for your answer. That is that Kinetic Energy is a result of 1/2 Mass times the Velocity SQUARED. It's rather obvious that a lighter bullet loaded to maximum pressures will produce MORE Kinetic Energy than a heavier bullet. BTW, study muzzle energy tables and you'll see this is true. Then remember that bullets exiting the cylinder also carry Kinetic Energy and you'll have the core of your answer.

I have seen with my own eyes a Model 66 with six-inch barrel and a forcing cone split at the flat spot. A friend of mine owned the gun. This was about 30 years ago, we were more foolish then, and we did a lot of experimenting with hot handloads and bullets of every weight. The 66 was his only .357 at the time. He got rid of it once the forcing cone split. It made me extra careful when looking at used K-frame .357s.

Cheers,
Whisper

Thanks for posting. That's the first one I've heard of.

In the computer age with computer aided design (CAD) systems we can shrink the safety envelope down to a bare minimum. I think we're not leaving enough of a safety factor. If we look at the older Japanese motorcycles of the late 60's to 80's they were heavy and over built that's why most of them are still running today. Now take the Chevy small block in the late 80's when they got the hair brained idea to cut costs they thinned the cast iron way too thin on the engine blocks. They didn't use the stress analysis that's on the CAD system nor did they think about the heat expansion. It's not only the CAD system it's common sense too. Today most manufacturers have eliminated there inspection departments too. They open up there tolerances beyond what they should be too. One part is smaller or larger and then by the time the assembly is put together it's way out of tolerance. Every manufacturer is under pressure to meet the production numbers to meet the demand from its customers. Now what do they want quality or quantity?

Funny there's never enough time to do it right the first time, but there's plenty of time to do it again go figure.

I don't think it's a coincidence that S&W dropped all the K frame 357's from their production leaving a few 38 special K frames and a lot of 686 models.

Meanwhile, the J frame 357s -- without the FC flat -- are still being produced.

Flat or no flat, the forcing cone on my M-60 .357 is much thinner than the ones in the M-19/66's. The factory's ability to constantly improve, and properly heat treat the steel is why the 60's made now can withstand regular use of full power ammo, including 125's.

The cracked forcing cones, while not nearly as common as the internet makes them seem to be, was enough to cause sales of K frame .357's to drop off and sales of the 596/686 to pick up, not to mention that an L frame is definitely more comfortable for the average shooter to use with full power ammo. Add to that, S&W had to stay competitive with Ruger's GP 100 and it's easy to see why they stopped production of most K frame guns.

I don't have a K frame, so I can't compare it, but is the FC really thicker than on the M60?

I'm talking about the minimum thickness at the thinnest point on the flat as that's the weakest point and only the weakest point counts.

No, it's even a bit thinner than the flat, and that is what I am pointing out. It is very thin all the way around the barrel shank where it sticks through the frame.

The chamber walls are .054" at their thinnest point, which is really quite thin, yet they can withstand constant use of full power ammo as well. The thinnest point of the chamber walls is approximately the same thickness as the barrel shank, but I can't give you an accurate measurement of the shank because I cannot get my calipers in the window straight enough to measure properly.

As far as the chamber walls go, they are as thin or even thinner than the thinnest point on my model 25's at the bottom of the bolt notches, yet you will constantly read posts on here and elsewhere saying how thin and weak the cylinders are on M-25's, and how one should never load the .45 Colt warmer than factory loads for fear of blowing one apart. The point is- with proper heat treatment, the steel can handle the loads.

As a side note on the 25's here: I know better, and I well know of John Linebaugh's reports on this subject, plus I have actually put mine to the test with some of his warmest loads and they handled them fine.

In a former life as an engineer, I got involved with the field of finite element analysis.

This is a computer science technology for analyzing forces on mechanical devices (it can also be used for heat flow).

Anyway, the technology to simulate the stresses on a cylinder or forcing cone has existed for a few decades.

It started in the Aerospace business, but is used these days for automotive part designs and other mechanical structures.

I assume the gun companies use the technology -- they certainly could.

It would be much easier to model the stresses on a cylinder knowing the pressure the cartridge would exert -- although knowing how the forces built up and decayed over time would be a bit difficult.

It would be much trickier to determine the peak forces on the FC given the impact of the bullet -- especially as it would vary with bullet type as well as velocity and powder load.

The comment someone made about the cylinder being slightly out of alignment with the barrel resonates with me also. I could see the peak impulse on the FC being higher and unbalanced if the bullet hit it slightly out of alignment. More likely to break.

Another factor is temperature.

If you read on the Freedom Arms forums, you will see that even their overbuilt Model 83s have had failures with some powders and light bullets due to overheating and melting at the FC and barrel throat.

Dave

It took me four decades before I purchased my very first s&w handgun. I been a ruger guy for four + decades. I been shooting stout magnum loads for most of my handgun experience at first. A magnum handgun is a magnum handgun what are we supposed to shoot out of it? We talked one night about how much of a hot load could my ruger SBH take. We were young and after the biggest bang and largest flames we could cook workers on. I was about 1 grain over max load. I had two 12" flames on both sides of the cylinder and a 15" flame out of the barrel. Thank God I didn't load up too many of these. The guys shooting on both sides if me left. I was probably near the proof loads ruger shoots to test each revolver. Other than tightening the grip frame screws after each outing I had no problems.
I don't think any other 44 mag could handle these loads other than the redhawk. Now I got into collecting a few S&W because of the s&w story on the history channel. I wanted to own some s&w history. I was always attracted to the n frames anyway. I know the limits on the s&w revolvers and not to abuse them. That's what my rugers are for anyway. I shoot my s&w with mild loads. I don't abuse handguns anymore. I'm a registered handgun offender. I'm sorry I did what I did in the past I do regret it. I baby my handguns now my wild and crazy days are over.

Cal44-

I appreciate your imput here.

I own an 83. I know that Bob Baker has posted (and I've corresponded with him about this as well) that they were seeing a lot of problems with guys using Lil'Gun in their guns due to the extreme heat it produces compared to other magnum pistol powders. I no longer use it in mine because of that. outside of that, I know of no other issues of any kind with an FA 83 other than the early models with replaceable forcing cone inserts, which were later dropped as they improved their own heat treating methods to the FC.

I understand what you are saying about the chambers etc, but my point is still valid- most everyone said that the chamber walls were to thin on a 25 and would blow with warmer hand loads due to being so thin over the stop notch, yet no one complains about that issue with the 60's and they are no thicker. It all comes down to heat treating of the steel for strength. The same holds true for the forcing cone. Even though the way the stress is applied to the FC is different than it is against a chamber wall, it is still applied exactly the same to the FC whether it is a 60 or 19/66.

I bought my 454 Casull Freedom Arms back in 1986. Back then, FA was touting tests where they put the maximum amount of powder they could fit into the 454 case for all types of powder on the market to prove they couldn't blow up the gun.

Of course they tested the gun on a rest surrounded by sand bags and with the trigger pulled by a cable from a distance.

I don't know if you get Handloader magazine, but Brian Pearce has written some oustanding articles on both S&W's and Rugers over the years. You'd be surprised what both can take when tested in a lab with "proof" loads. the Redhawk is quite a lot stronger than the SBH, and will take loads that no other revo outside of an FA will take with ease. It is truly a beast of a revo.

Your comments on the flames at the muzzle reminded me of another article in a past issue of Handloader by another author. Many believe that flames at the muzzle are a sign of high pressure or overloads, but they generally have nothing to do with it, yet it's quite hard to get folks who believe that to accept the truth. The flames are caused by hot gasses hitting the oxygen rich atmosphere and re-igniting. The article was backed up with laboratory tests/data.

I have articles in several old gun mags about those tests, and have actually watched a video that was made of one of the tests. I believe it was done by Guns and Ammo's Jan Liboural, and possibly Gary James, though I can't recall that for sure. IIRC, they were stuffing as much Bullseye into the case as they could seat a 240 grain bullet over and firing the gun. It held and didn't even have a bulged chamber wall.

I will take it off your hands for you...

The cylindrical shape of a barrel will distribute the pressure load equally around the circumference. As the pressure from increasingly hotter loads rises, the thin section is subjected to an unequal load. This is because the K frame forcing cone is cylindrical internally but the outside diameter has a reduced section. As the pressure wave moves through the wall thickness of the forcing cone the pressure doesn't change but the material becomes thinner at that spot, i.e. unequal load.

However, I agree with the others that have said this situation is greatly exagerated. If it were anywhere near as common as stated, there wouldn't be any .357 K frames left. The truth is there are thousands of them floating around.

The case has been made that the failures were due to light bullets at high pressure. The failures were possibly exacerbated by lead fouling in the fc that was not removed before shooting hot loads, which increased the pressure. That seems the most plausible, in any case I'm not concerned about shooting 158 grain magnum loads in my Model 19.

One of the reasons I like shooting revolvers ove autos-the flames that come out of the side. Wicked cool and elevates you head and shoulders above the gangbangers with those 40's.

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Forum consigliere

I had the forcing cone crack in a gun that had never fired a single lead bullet.

It took less than 1000 full-powered 357 loads to crack the forcing cone on my Model 19.

Several years ago I had S&W do an action job on my 66-6. It came back very nice, with a note that said:

"Sir-

Practice with .38
Carry .357"

Sorry you bought it??? Are you letting others talk you into and out of what you like? I, too, have read all the blather about forcing cones, weak frames, ect. over the years. Many post about "I read" or "I heard" but VERY FEW have actually experienced any trouble with their K frames. I won't put a 125g "hot" load in any of my 357's simply because I don't find it necessary to run my guns at full throttle all the time and beat the **** out of 'em! I'm not the least bit interested in finding out what it takes to break stuff.

All guns are a compromise of some sort...no one gun does it all. Your 3" 66 is one of the best all around 357's ever made and don't let anyone tell you different. I mean really...what do you need to do with it that a 158g load won't do? If you're trying to knock down concrete walls you need something else anyway.

P.S. My 3" 66 is staying right where it is along with all my other K frames!

And the size of the cylinder gap would be another variable.

I use a 140 gr bullet at 1000 ft/sec. My guns are for home defense so I don't want to blow our ears out with big .357 loads.. This is either a low end .357 or a .38 +P+. I would feel comfortable shooting thousands of these through my .357 and not feel like I was being hard on the gun.

+1 to rwsmith. I hand load so I can load what I want...that's why I load. I find .38+P to be a very nice round for all around practice and plinking in my short barreled .357's...but I also practice with and shoot a lot of medium 158gr HP .357 loads for carry. The 3" 66 is a smaller magnum that is not fun to shoot with a full 158gr magnum load...the gun is fine...it's my hand and ears that complain!

You don't have to baby your 66...just don't abuse it...any regular factory 158gr .357 loads will be fine and I think you will find them to be plenty stout. Again, the 38+P or +P+ is sweet.

This is all JMHO but I have owned and shot them for years.

Is it safe to assume that running light .38 loads (125gr TC lead or 125gr JHP, either doing ~800fps) through a 66 is never going crack the forcing cone unless the cone was defective and destined to fail no matter what?

I keep reading statements that S&W improved there heat treat capabilities. This makes me curious because as a custom knife maker I am very into heat treating and metallurgy and even correspond with a couple of metallurgists. I have not heard of any great improvements in heat treating of steels in the last 50 year. Ya there are now digital controls and better inert atmosphere ovens, but the process has been well understood for a long time. The have been no great improvements in carbon steels either. This is not true with stainless as CPM type technology has made some improvements there. But, I doubt they use CPM in their stainless models due to expense. (CPM is taking a molten batch of steel and spraying it in an inert atmosphere which forms small "BBs" of very uniform steel which are then heated and pressed together to form a very uniform solid billet.)
So, has S&W been working with antiquated equipment until recently??
I find it hard to believe that S&W has recently discovered some great HT for the relatively simple steels used in steel revolvers. Where do these statements information come from? Where and from whom can I access any real facts on this?

I am not talking about the progress in stainless or the light exotic alloys like titanium. Just the steels in blued guns like the K frame, J frame and rumored difference in the model 29 frame. Does anyone have any facts and where did you get them???

If you are referring to the posts I have made here, re-read them. I was talking about SS and the model 60 in particular. I mentioned the 25's for the sake of comparison in chamber wall thickness to the 60.

BTW- I see you either were, or are a Marine. Thank you for your service to this country.

Yes, 125 grain .38 loads will be safe to use.

I think the problem with cracked forcing cones and frame cutting on K frame magnums is due to erosion, and not mechanical impact. At least, at first.
Erosion is caused by hot gasses at high speed.
With lighter bullets moving at higher velocities, the bullet base clears the gap sooner, since it takes less time for the faster bullet to cover the distance. The bullet acts like a sliding valve, opening the gap when the base passes. The pressure in the chamber starts to drop before this happens, but with a faster bullet, the pressure has not had as much time to decay. The higher pressure, hot gasses are more erosive than would be the case with heavier, slower bullets opening the gap after more time in the ignition sequence, when the pressure, and maybe the temp are less. After the steel has been weakened by hot gas erosion, it would then be vulnerable to mechanical damage by the bullet impacting the forcing cone.

Best,
Rick

I've owned and shot K frames for years. My agency used them up into the mid 1990s. We shot factory loaded 125 gr. .357 magnum hollow points exclusively for qualifications and practice, and many of the agency issued 4-inch Model 19s were abused for decades. Some of my fellow officers rarely cleaned their 19s, much less worried about leading up the FC that could cause excessive pressures.

I only witnessed one cracked FC in the five years I shot revolvers before we transitioned to semi-autos, and that was because an officer next to me on the firing line sprayed me with lead shards during a qualification. After taking a chunk of lead in my left forearm and cheek during a course of fire, I notified the Range Master of the issue, and he confirmed my neighbor's cracked FC. Like I said, these Mod 19s had been through the mill for decades, firing hot, light rounds, and many had been neglected and ill maintained.

The great majority of those 19s never had a problem, despite age, wear, and neglect. Simply because I worked in the backcountry and preferred a short barrel, I carried my personally owned and well maintained 2.5 inch Model 66 that fired the same hot 125 grain loads. I never had problems. I still load 125 gr. .357 loads in that 66 that I carry hiking, and use for HD, but I practice with .38+P to save wear and tear on me...not the handgun.

I'd say keep your 66 or 19 well maintained, and you should be able to shoot magnum loads without worries. I sure wouldn't lose any sleep worrying about cracking the FC, and if you are worried, then simply practice with milder loads.

Not, looking at anyone persons posts. I just keep hearing about S&W's improved HT and I don't get it for any of the BLUED steel guns. Can't believe they have been using that antiquated of equipment, low grade carbon steel or methods since a long time ago. Plus I recently took hardness test on all my blued Smiths and the all read between 79 and 82 Rockwell B, which within the range of regular mild steel with no HT. Very near dead soft. 41xx type steels is a very common steel for recievers and it and its HT methods have been around for a long time.

I believe a lot of the improvements in stainless have been in machineability. How much has been discovered in the HT of stainless tool steels in the last 25 years is debatable. There have been some improvements in high end stainless tool steels. I also notice that my 629 attracts a magnet very strongly which tells me it is martensitic and can be heat treated.
Thank you, Semper Fi

I've read that to introduced the model 19 in 1955 they improved heat treatments to strengthen the K frame. Probably the only improvement since then has been better controls. I suppose this carried over into all of their steel guns.

Same thing went for the 44 magnum when they were developing it. It has been written about extensively by many well known authors over the years.

That would make sense especially in regards to time frame and HT equipment technology.

A steel like 4140 would have to be annealed after forging to take care of the brittleness caused by grain growth cause by the necessary forging temps. A oven and control improvement here would do a lot.

To properly anneal 4140 you must take it to 1500f and cool 25 per hour to 1225f and then air cool. You would want to do this in an inert atmosphere to prevent decarb.

To further HT you would have to harden by some type of quench (water mist or oil) after a 30 minute soak at 1500f. Then temper.
This too would take an inert atmosphere to prevent decarb.

Then there would be the temper. Temps over 1000-1100f would take it to the lower RC ranges (or 80s Rockwell B) They would want them fairly soft as harder is brittler. Tensile strength goes down as hardness goes down. The ability to take repeated stresses would need this state.

SAE 4140 Steel Tempering
Tempering
Temperature Hardness
Brinell Hardness
Rockwell Tensile
400°F 200°C 514 HB 55 HRc 297 KSI
500°F 260°C 477 HB 50 HRc 243 KSI
550°F 290°C 461 HB 48 HRc 235 KSI
600°F 320°C 444 HB 47 HRc 225 KSI
650°F 340°C 429 HB 46 HRc 217 KSI
700°F 370°C 415 HB 44 HRc 210 KSI
800°F 430°C 363 HB 39 HRc 182 KSI
900°F 480°C 331 HB 36 HRc 166 KSI
1000°F 540°C 293 HB 31 HRc 145 KSI

It does not make sense to use a different Heat treatment on some frames as most of the process is the same except for temper and why temper some to a weaker state? Once they had the improved technology why wouldn't they rabidly change the process for all their frames to the same higher standard? It wouldn't take a huge oven by industrial standards to do a lot of frames.

I build my own digitally controlled electric HT oven capable of an inert atmosphere and it wasn't very expensive or difficult. A room sized unit wouldn't be that difficult or super expensive and you could hang a ton of revolver frames in it.

PS
The thing about the martensitic Stainless used things like receivers is that the temps for annealing and hardening need to be higher (in the 1850f range) because the high amounts of chrome inhibit the movement of the carbon. The nice thing is that most of them only need an air quench as the speed necessary to cool is slowed by the high amounts of chrome again.

Ya, I am a steel geek!

I love materials, I got to work with many as a designer in a research lab. Especially for the activated carbon group that used high temps and corrosive environments. Made some reactors out of Inconel X one time.

Ya, I have worked with Inconel alloys too. Interesting metal, extremely red hard (retains it shape and strength when red hot) Expensive too, because of the high amounts of nickle in it. In the oil industry it is often used for hangers and attachments in furnaces.

You must have got to play with some interesting materials.

It's possible that the 'flat' failed not because it was thin, but because it was a transition of material thickness that would concentrate points of stress. 'Stress risers' they are called.

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"He was kinda funny lookin'"