Cracked forcing cones cause?

[DWalt]

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?

 

[OKFC05]

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.

 

[Cal44]

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.

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.

 

[OKFC05]

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.

 

[Jdavis]

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.

 

[Snapping Twig]

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.

 

[2ndAmendmentNut]

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.

 

[sac-gunslinger]

I bought a 66-4 3" a few weeks back and it was pricey. Sure hope it does not crack or I am out a bunch of money and a gun I can't get parts for. A little sorry I bought it.

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.

 

[2ndAmendmentNut]

I have a Lewis lead cleaning tool on the way along with a bore light. I will make sure I keep the force cone maintained. I really do like this firearm a lot, it is a tack driver. There is no need for me to run high power rounds through it so I won't. Thanks for the reassurance.

I have a few boxes of 130 grain .38 special, I take it that these are OK to run. Maybe I should avoid this round also?

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.

 

[Gun 4 Fun]

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.

 

[Nemo288]

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

===
Nemo

 

[Snapping Twig]

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

===
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.

 

[scooter123]

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.

 

[Whisper]

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.

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

 

[Gun 4 Fun]

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.

 

[BigBill]

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.

 

[Cal44]

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 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.

 

[Gun 4 Fun]

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.

 

[Cal44]

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.
.

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.

 

[Gun 4 Fun]

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.

 

[Cal44]

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

 

[BigBill]

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.

 

[Gun 4 Fun]

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.

 

[Cal44]

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.

 

[Gun 4 Fun]

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.

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.

 

[Gun 4 Fun]

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 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.

 

[K31]

I bought a 66-4 3" a few weeks back and it was pricey. Sure hope it does not crack or I am out a bunch of money and a gun I can't get parts for. A little sorry I bought it.

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

 

[desmodue]

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.

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.

 

[CAJUNLAWYER]

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.

 

[Warren Sear]

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.

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