Magnum loads in .357 K frames

[Leadslugga]

I was reading about the K frame Smith magnums (19 and 66) online, and read that you should avoid firing magnum loads with other than 158gr bullets. The site I was readings said that the forcing cone is thinner on the K frames, and shooting lighter bullets can cause it to wear/become damaged. It went on to say that this is why they no longer make a .357 K frame.

Is this true? I always heard that they went to the L frame because the K was not designed for continuous magnum use (practice with .38s and just load .357s for the real deal) and would eventually wear out, whereas the L was designed from the get-go to handle magnums. But if all this is the case, what about the model 60 and other J frame .357s?

Enlighten me.

 

[03protege]

Did they give any information on why the forcing cone would wear out faster?

I've read a lot about magnums tearing up these guns and making the mechanically loose but not anything about forcing cone damage.

 

[Leadslugga]

I read it on this site:

http://guns.wikia.com/wiki/S&W_Model_66

As you can see, the article is fairly scant.

 

[Leadfoot]

LSP972 can tell you all the details but the lower grain .357 rounds were notoriously hard on forcing cones in Smith K frames.

Doesn't mean you can't shoot them in a K frame, but a steady diet will cause damage.

 

[03protege]

Lighter bullets = more powder = hotter vapors?

That is the only thing I can see that would do it, would be interesting to know the exact reason why.

 

[Leadfoot]

Borrowed this from somewhere else but it explains it pretty well:

Cylinders long enough to accommodate full charge 158 grain bullets provide a great deal of free space when shorter bullets are used. A very popular loading for the .357 magnum was for the 125 grain jacketed bullet. In the early days, this was a great combination with high velocities and excellent terminal performance. Today’s bullet designs offer equal or better performance from heavier weight bullets and over a broader range of velocities. The bearing surface length of the 125 grain bullet is shorter than the bearing surface of the 158 grain bullet. This difference means that as the 125 grain bullet leaves the case there is a gap between the leading edge of the bullet sealing surface and the cylinder throat. As the short bullet makes this jump, combustion gases and powder are permitted to blow past the bullet and prematurely escape into the barrel. The 158 grain bullet essentially seals off the cylinder as it leaves the case and enters the cylinder throat. More complete combustion of the powder is accomplished. Temperatures of the gas as it enters the barrel are lower and the combustion environment in the barrel is not oxygen rich as is the case for the prematurely escaping combustion gas. Checking the dimensions of my 19-3 confirms that for the 158 grain HP bullet, the leading edge of the bullet is engaging the lands as the base of the bullet has just left the case mouth and is flush with the cylinder throat. For the lighter HP bullets of 115 to 125 grains, there is a gap of approximately 0.15 to 0.12 inch, respectively.

The problem with the gap of the shorter bullet is that it permits excessive hot burning gases to escape past the bullet into barrel throat. This superheats the surface of the barrel throat with the hot gas plasma. Still unburned powder blasts away at the barrel throat surfaces and the repeated impact of the high velocity bullets on the lower surface of the throat region result in erosion of the throat in this area. One might question why the impact and erosion is predominantly at the six o’clock position. Recoil. Longer bullets are guided by the cylinder throat and thus are not impacting the lower barrel throat as with shorter bullets. The shorter bullets have a longer “jump” from the case mouth to the barrel lands and thus pick up more velocity prior to engaging the rifling. This causes a greater impact force on the rifling contact area. Another detrimental effect is the flame cutting of the frame as these super hot gases escape from the cylinder-barrel gap. This problem would be present for short bullets in all models of firearms.

Based upon reports of those who have seen examples of throat cracks, several characteristics appear common. First, erosion at the six o’clock position in the throat is almost always present. Most describe this as “peening”. Second, the weapons have generally not been thoroughly cleaned after use. Deposit of lead and bullet fouling are present in the throat erosion region. These deposits can create conditions for chemical stress corrosion and initiation of microscopic cracks in the steel. Third, most of the weapons have other signs of excessive use and wear, possibly from overly hot loads. Very small to large cracks can form at this particular point, the six o’clock position, in the barrel throat. The impact force of the bullet on the rifling would increase the probability of a problem in this region.

 

[03protege]

Thank you sir, that is some good info.

 

[Leadslugga]

That explains it pretty well, thanks.

Second question!

I read that over time every revolver needs a timing job. I've shot thousands of rounds through my 686, mostly 38spl, but hundreds of 125 gr mags as well. At what point should I start to be concerned with the cylinder getting out of time, and how does one check for this?

 

[Leadfoot]

That explains it pretty well, thanks.

Second question!

I read that over time every revolver needs a timing job. I've shot thousands of rounds through my 686, mostly 38spl, but hundreds of 125 gr mags as well. At what point should I start to be concerned with the cylinder getting out of time, and how does one check for this?

How to check: READ CAREFULLY

1) UNLOAD YOUR GUN

2) CHECK TO MAKE SURE YOUR GUN IS UNLOADED

3) CHECK ONCE AGAIN TO MAKE SURE YOUR GUN IS UNLOADED

4) DON'T DO THIS WITH A LOADED GUN

5) Close the cylinder and thumbcock the hammer.

6) Shine a flash light at the rear of the cylinder from the side.

7) Look down the barrel from the front of the gun toward the rear of the gun and look to be sure that the cylinder and barrel are in alignment. Do this for EACH cylinder. If any are NOT in alignment, don't shoot the gun and take it to a competent REVOLVER smith.

 

[Leadslugga]

That what I imagined the process would be. I didn't know how precise the measurements needed to be. I'll "eye" my revolver next time I clean it.

 

[Gus McCrae]

I didn't see it, but if my understanding is correct, the forcing cone on a K frame has less meat which makes it more prone to cracking due to the gasses described above. S&W beefed up the forcing cone area (over the K frame) to address this issue.

N frames aren't as effected, Rugers aren't as effected, I don't think Taurus is as affected. They still may be susceptible to the heating due to gasses, but the cone area is beefier, so it resists cracking better.


That's my understanding.

 

[Leadfoot]

Eyeing it is close enough for a non professional. Now, if you notice your gun starts spitting lead out of the cylinder area, this is a good sign the timing is amiss.

 

[nickatnite]

I read it on this site:

http://guns.wikia.com/wiki/S&W_Model_66

As you can see, the article is fairly scant.

Yeah, I wanna believe that website... Here is their disclaimer:
Our MissionEdit
At Wikia, we strive to...
Bring out the “expert” in everyone.
The collaborative web movement has shown us that many minds are better than one. Wikia provides a collaborative publishing platform on which everyone - really, everyone - can share their passion and knowledge on subjects that don’t fit into the strict model of an encyclopedia. By doing so, we unleash the inner expert in everybody.

 

[ericlosh]

I did alot of interent reading on this issue as well since my first revolver was a model 19. I hear the model 66's are less susceptible just due to the type of metal, and the problem over all is very minimal and blown out of proportion by the internet, think glocknade. Higher grain magnums are better to be shot out of your k frame on a regualr basis, and leaving the real hot stuff for self defense. You'll hear all these ratios about how many magnums to shoot, i wouldn't be concerned, stick to 140-158(158 grain magnums are more recommended) grain magnums and things should be fine. I'd shoot only magnums through both my model 66's if i could afford it, and many shooter do shoot alot more magnums through their k frame with no issues. I personally would leave the real hot stuff for self defense, but if i couldn't find standard loads i would put hotter stuff through my guns.

The biggest concern i found was cleaning the the forcing cone, buildup of carbon along with hot loads was what would lead to failure, and the issue is nearly non existent with proper cleaning. I think this is an issue that is kind of blown out of proportion cause everyone wants to know all the details so all the stories get passed around a little to much. The combat magnums are excellent guns and very fun to shoot .38 spc and .357 magnums out of.

 

[Gus McCrae]

I don't disagree that there are ways you can take better care to ensure you get the most out of a K frame. I think they are sweet shooting guns. My mother has my dad's 19 and it's a great gun. Still, I don't think the L frame would have been made if there wasn't some issue with the K frame. S&W would still be making them too.

 

[CEHollier]

Am I understanding correctly. I own a 686 L frame. It can better handle the lighter bullets because it was initially built for magnum rounds. I have shot at least 300-400 rounds of 110g magnums through it without any issues.

 

[Leadfoot]

Am I understanding correctly. I own a 686 L frame. It can better handle the lighter bullets because it was initially built for magnum rounds. I have shot at least 300-400 rounds of 110g magnums through it without any issues.

Correct. The L Frame Smith's do not suffer from the issues found with the K Frame models.

 

[ericlosh]

I don't disagree that there are ways you can take better care to ensure you get the most out of a K frame. I think they are sweet shooting guns. My mother has my dad's 19 and it's a great gun. Still, I don't think the L frame would have been made if there wasn't some issue with the K frame. S&W would still be making them too.

Thats correct, but if the problem was that bad, then the production of model 19 & 66's would have ended much sooner. I dont think the model 19/66's problems are that bad. The model 19/66 seems to have just ran a normal production/service life. I also imagine most of them were made for LEO and when they switched to glocks and other modern designs, they still kept making the 19/66 for a while. I don't think there are too many people that feed these guns the amount of high power magnums required to break them, there are enough people that dont clean their guns that well though. Even then most people feed their magnums non magnum rounds (38 spc .44 spc) just because of costs. Point is that I don't think OP has to worry about a thing and if he sees a good price on a combat magnum, get it! Excellent guns.

I've had my model 66's for less than a month and have put roughly 50 magnums through each and wold have put 3x that if i could afford it. Those college expenses man. I'll probably end up shooting my 2.5" one more just because i plan on carrying that gun regularly. It feels great shooting magnums out of that thing.

My typical magnums are federal 158 grain .357 magnums.
I may switch to fiocchi (140 or 148? grain) magnums instead as my local range stocks em at the same prices as walmart's federal and I'd prefer to give them the buisiness.

 

[ericlosh]

Ive never heard the term full house magnums before, i assume they are the hot stuff? Those i do avoid shooting.

 

[Leadslugga]

Yeah, I think people just like the term "full-house magnums" because it helps to highlight the difference between .357 and .38 spl.

I guess the term could have a special meaning to a handloader. I mean, when I handload .357 mags I don't always load them "full house."

You can load it well over .38 spl power but still well under the full .357 power. In that case I suppose you would not be shooting a full house magnum.