K Frame cracks

Hi, can someone enlighten me about K frames cracking from shooting too many .357 magnum loads? Is the 13, more prone to this than the 65, or 88? I am currently looking at 65's, and don't want to ever have this issue. Any, feedback would be appreciated! Thanks, Bob

Stick with 158 grain bullets and you should be fine.

Frank

That makes the newer one's with the lifetime warranty look more attractive and with the peace of mind, less expensive. Kinda like an insurance policy.

The forcing cone cracks result from shooting light 357 Magnum bullets in the K frame and like others have said the 158 grain bullets will not cause you any problems.

Two things to keep in mind:

1. Cracked forcing cones were, and are, a rare phenomenon. Although it got widespread coverage, it has really happened a very few times, compared to the vast number of magnum K-frames built.

2. Although some cracks were likely caused by improper assembly, the most commonly accepted cause was shooting 125 gr. bullet loads; however, not just a few of them, or even a few hundred, but thousands.

While someone who shoots a heavy volume of light-bullet maximum-pressure loads should be concerned, for the vast majority of K-frame shooters the cracking issue is really a non-issue.

I don't feel any need to shoot bunches of higher end 357 loads in the likes of a Model 65. 38 +p is about all I ever need in mine.

sourdough44 said:

I don't feel any need to shoot bunches of higher end 357 loads in the likes of a Model 65. 38 +p is about all I ever need in mine.

Click to expand...

Amen

I still use the old FBI load for defense in our J and K frames.

Proven round even out of a snubby. Even better out of 4 inch.

Pisgah said:

Two things to keep in mind:

1. Cracked forcing cones were, and are, a rare phenomenon. Although it got widespread coverage, it has really happened a very few times, compared to the vast number of magnum K-frames built.

2. Although some cracks were likely caused by improper assembly, the most commonly accepted cause was shooting 125 gr. bullet loads; however, not just a few of them, or even a few hundred, but thousands.

While someone who shoots a heavy volume of light-bullet maximum-pressure loads should be concerned, for the vast majority of K-frame shooters the cracking issue is really a non-issue.

Click to expand...

I love my K frames, but if it was such a rare occurence, why'd they get rid of them in .357? My 686 will never feel as nice as any of my K frame .357's, but I have a bit more confidence in shooting magnums in my 686 over the K's.

The bottom of the forcing cone on the K frames is flat instead of perfectly round, making it slightly thinner at that point, and that is where the cracks happen. Because of the frame size this design was necessary in order for the cylinder to close.

As others have said, this is not a common problem, and is generally associated with a steady diet of full power magnum loads with lighter bullets over a long period of time. Most folks I know shoot a higher percentage of .38's than .357's in their K frame magnums, and use heavier bullets with their .357 loads.

You have more to worry about from an alien invasion from Mars...



This Police Trade-In 66-2 saw a documented round count of over 10,000 rounds of Federal 125 JHPs during it's service life.



It's still one of my favorite field guns. Like tens of thousands of these guns built in the 70's & 80's my 66 still soldiers on....

Drew

Since it hasn't been mentioned yet I'll point you to the area of concern and the cause. Take a look at the barrel extension inside the frame window. If you look close you will see that there is a flat machined in the bottom surface to clear the gas ring on the cylinder. This thins the forcing cone in this area and it's typically where the forcing cone will crack.

Now, as for why they crack with lighter bullets, this is my theory and I'll admit that it's quite possible that I'm wrong. It's a function of the Kinetic Energy carried by the bullet as it exits the cylinder and enters the forcing cone. With a light weight bullet that lower mass will allow it to develop more velocity within the chamber of the cylinder. Put a 5000 horsepower engine in a dragster that weighs 5000 lbs. and you'll have a dragster that probably runs the quarter mile in about 12 seconds. Put that same engine into a 1300 lbs. dragster and you'll have a dragster that runs the quarter mile in about 6 seconds. Quite simply a light bullet can get up to speed a lot faster than a heavier bullet being pushed by the same amount of pressure. Since Kinetic energy is a function of the Square of the velocity times the Mass, this means that a light bullet can produce more Kenetic Energy than a heavier bullet. End result is that light bullets crack forcing cones a lot more frequently than heavier bullets. Note; this ONLY applies at Magnum level pressures, the 38 spl. and 38 +P operate at such a low level of pressure in compaison that forcing cones don't crack when shooting 38 special loads even when +P and featuring a light 125 or 110 grain bullet.

Now, a bit of History. The K frame was originally designed as a light weight revolver specific to the 38 S&W and 38 Special, both which operate at a relatively low pressure and both with featured bullet weights that are "heavy" for the caliber when compared to modern centerfire calibers. While metalurgy has improved a lot in the past 100 years there is a real limit to what you can do with even modern steels heat treated using the most scientific methods. IMO the 357 Magnum K frames have always been rather close to the limit of what can be done with modern steels and using a light weight bullet is all it takes to "tip" some barrels into failure. As for why, even with the best heat treating furnaces and the best controls, you will see a variation in hardness of between 2 to 3 points on the Rockwell C scale. While that difference isn't much in the broad scale, that small difference is just enough to cause some barrels to fail quickly and others to not fail at all. Simple fact is that with the 357 Magnum every single K frame is very very close to the point of failure with a light bullet and it's pure luck if the forcing cone doesn't crack. In addition just a 0.003 inch difference in the depth of that cut for the flat may be enough to mean the difference between failure and longevity. As for why this issue wasn't discovered when the Combat Magnum was first introduced, it's actually fairly simple, at that time the common 38 caliber bullet weighed 158 grains and the "light" bullet in this caliber was a 147 grain wadcutter. The 125 grain loads didn't hit the market until much later in the 70's and that is when the forcing cones started cracking. BTW, I've read that in some cases it only took 50 rounds of a hot 125 grain 357 Magnum to split a forcing cone, so I don't think it's safe to assume that it takes years and many thousands of rounds to have this happen. Some get lucky and some don't.

Personally, it's not a concern for me, my wrists aren't in the best of shape and I find the K frames just too light in weight for the 357 Magnum. For me the 357 Magnum only starts to be tolerable in the L frame and for lots of shooting I have a strong preference for the much heavier N frame.

I was wondering what made cracking more likely with the lighter weight bullets......

I am aware of a cracked forcing cone in a K-Frame .38 that was shot with standard .38 Special loads and it was reported on this forum although I have lost the thread. The handgun was already well shot before the incident occured.

It has also been reported here that another "suspect" of forcing gone cracking was leaded forcing cones that were not cleaned sufficiently.

Another suspect is the hard, ball powders which burn very hot, like H-110/W-296. And it is a fact they will affect handgun metal because these powders do cause visible wear on the top-strap (called flame cutting) and the outer edges of the forcing cone. Some of my K and N frames exhibit this.

And, as Sebago Son has illustrated there are K-Frames that just are not affected by cracked forcing cones with any load.

In Colts, the "D" Frames (if I have this right) as in the Police Positive and Detective Special have a thinner all-the-way-around forcing cone and I have heard, but have not seen, that they too can crack. What loads did it I do not know but when the +P .38 Special loads came out Colt did state not to use them in those guns.

I am not deep into metallurgy but I was once an aspiring welder with some college training in that direction. Even the best (back then) metal producing program can create odd, or indiscriminate examples that just won't perform as they should.

It is possible some of the K-Frame .357 barrels/forcing cones fell into that "genre", they just didn't come out as well as the others and were prone to failure.

My use, and I have a few K-Frame Magnums, is that I load .38 Special loads in .357 Magnum cases for practice. I load lead 158 SWC's to magnum velocities in .357 Magnum cases.

I see no advantage to a 158 grain jacketed bullet over a cast one in a K-Frame.

However the "non-reloader" has to use factory ammunition and as such, supposedly the factory 158 jacketed rounds "should" be safe in a K-Frame. There is a small variety of "cowboy" .357 Magnum loaded ammunition that is a 158 grain lead bullet at .38 Special velocities for the Cowboy Action Shooters as well. It should produce a 158 grian lead bullet at about 800 to 900 fps.

I will admit to being "bummed" by this knowledge. I specifically wanted to dedicate my K-Frame .357s to 110 and 125 grain loads going as fast as safely possible...

Their light weight would be well suited by the lesser recoil of the lighter bullets.

This topic comes up about once a month. The K frame magnum can't handle light grain magnums very long before the forcing cone cracks. While I have never seen this other than the internet the issue is not just K frame magnums. Shooting high round counts of 125 gr 357s at high velocities over 1500 fps is hard on any revolver. I will give examples of a K frame spliting a force cone and yes a Ruger GP100. The Ruger GP100 is supposed to be built "like a tank" and can take thousands of full power light weight magnums. Here are the pictures.

K frame magnum cracked forcing cone

Ruger GP100 cracked forcing cone

Here is my point. No matter what 357 magnum a person has if a person shoots high round counts of full power 125 gr magnums a person can expect erosion of the forcing cone, flame cutting and possibly a crack forcing cone. Here is a good description of what happens shooting full power 125 gr magnums.
According to several different sources, the shorter 125g (and 110g) bullets have two problems. First is that they exit the cartridge case much sooner than the longer 140g+ projectiles. This means there is more time for hot propellant gasses to act on the topstrap and forcing cone. the standard 158g bullet builds up more pressure and (apparently) moves much slower from cylinder to the rifling, which burns more propellant inside the case & cylinder. The lighter bullets also tend to impact the forcing cone harder because of their speed from cylinder to rifling. This tends to "hammer" the metal more than the heavier bullet. Bullets of 140 grains or more have sufficiently long bodies to reduce the gas cutting and are less prone to impact damage to the barrel.
I have seven 357 magnum revolvers. From three K frame magnums, one L frame 686, one Blackhawk and one Ruger Service Six. I don't shoot any lighter than 140 gr magnums. Reason is what the above description of what happens shooting the full power 125 gr magnums. There are so many better options made by ammo makers a person does not have to abuse their revolvers anymore.
Howard

Sebago Son said:

You have more to worry about from an alien invasion from Mars...

Click to expand...

Maybe.

In a lot of years of shooting S&Ws and looking at used ones, I have seen (in person) exactly one K-frame magnum with a cracked barrel. It must not be all that common.

But I wonder if this is what the OP means since he didn't say barrel (or forcing cone)? I have seen a couple cracked K-frames. Ones I can recall were a Model 10 and a Model 15. Both guns were repaired in the field, which I am sure S&W would never authorize, but "it happened." Frame cracks could be over-torquing at barrel installation, or maybe a defect in the metal, or other problem. (For example, is the frame faced square with the axis of the threads?) Both repaired guns were returned to service and still working when I lost track of them.

Does the same principle of lighter weight bullets loaded with full house charges apply to a 44 mag?? I have recently placed an order from a local licensed ammo manufacturer for a batch of 200gr Hornady XTPs with Lil Gun powder, (I forget the exact charge) that according to his handloading spec books is supposed to generate 1600fps.

Is this risky or can my 629-6 Classic handle it?

I would not load Lil Gun in any handgun here is a post from Bob Baker of Freedom Arms.

"We have seen numerous barrels damaged by using Lil Gun. According to customers, some had as few as 30 rounds using Lil Gun through them, some had several hundred. Before we figured out what was happening one customer had sent his gun in for a new barrel. Then 600 rounds later it came back for another new barrel.

A couple years ago we did a test with a M83, .357 Mag. using Hornady 180 gr. bullets. We loaded 50 rds. of three different loads. One was a heavy H-110 load and the other two both used Lil Gun in different quantities.

We fired the H-110 loads first, then cut off the threaded end of the barrel. Rethreaded the barrel and shot one of the Lil Gun loads then rethreaded the barrel and shot the last Lil Gun load.

We found even the light load of Lil Gun caused the gun to get extremely hot. The heavy Lil Gun load had the gun so hot the only place we could touch the gun was on the grips and they were very hot.

Under magnification the surface appeared to have heated to a point of flowing using the Lil Gun loads and the heavy load was worse than the light load. This is probably due to Lil Gun having about 10% more nitro glycerin in it than H-110."

Link to quote on another forum, it is reply number 12.

http://www.go2gbo.com/forums/index.php/topic,180437.0.html

In addition I have seen several posts of using it in .450 Bushmaster and .50 Beowolf loads where after 5 rounds of Lil Gun the barrel is too hot to touch while with 296 or H110 the barrel is only warm. YMMV.

Is this risky or can my 629-6 Classic handle it?

As I understand the problem (?) with the split forcing cones was only in K frames. Your 629 is an N frame and the N frame forcing cones are thicker than those on the K frames'.

I no longer feel the need to shoot .357 Magnum ammo in my K frames any longer, that is what my L and N frames are for. I do though load full power .357 Magnum ammo in all my revolvers for Self-defense though.

Round Count...

IF this is a real and wide-spread problem, then based upon servicing 50-odd 66's for a local PD over several years long ago, then the point of failure must be well over 5,000 rounds.

You'd have to be J.P. Getty to shoot that much factory 125 grn. JHP .357 Magnum these days.

Broken hammer noses (firing pins), bent front sight blades, broken rear sight slides, loose stocks, unscrewed extractor rods, lost thumbpiece nuts (and sometimes the thumbpiece too), cylinder stops and once, a broken hammer nose bushing, these things were all stock-in-trade to keep a Police Revolver in service. But I never saw one cracked forcing cone in the many years of supporting these guns in the field.

I guess they must have been happening someplace else...

The K-Magnum is a fine weapon with an superb history which has earned a long and enviable in-series record on a national basis and reigned as "King" in police holsters for more than 20 years. When they left the limelight it was because of the desirability of autopistols, not due to some defect in the design or issue with ammo compatibility...

I think I'd find something else to worry about and enjoy your fine revolver.

Thanks to everone's responses! I know that this topic has come up before, but now I am looking at 65's and 66's and don't want any possible problems. Chances are, that I would buy only 1 box of .357 ammo for self defense, then load my own. Standard .38's would work well enough for target shooting and plinking, which I load. ( use cast 158 gr. LSWC ) I just need to have a .357, and am not sure why. Thanks again! Bob