Rechambering S&W 10 to .357

[John Wayne]

I own a S&W model 10-7, a 4" pencil-bbl. K-frame .38 Special revolver. A post in another thread sparked my interest about having this gun rechambered in .357 Magnum.

Yes, I already know that S&W produced K frame .357 revolvers for many years--but I already have this gun, I like it, and it would probably be cheaper to rechamber it to .357 than to sell it and buy a .357 K frame.

I know that it is possible to rechamber some revolvers for more powerful cartridges. I have most frequently heard of it being done with guns that are notoriously overbuilt, like the Ruger Blackhawk. I also know that S&W discontinued K-frame .357s (but continues to produce the J-frame version).

Is this gun strong enough to handle firing .357 Magnum cartridges by just having the cylinder reamed out, or will I need a new cylinder? Or is the frame strong enough at all?

I plan to occasionally fire full-house .357 loads in this gun, but mostly target loads (158 SWC @ 750 fps) for practice.

Info on whether this can be done is appreciated. Also, if anyone can reccomend a place to do it that would be great as well.

 

[The Bushmaster]

Before you do it. Next time you happen to run across a S&W mod 19. Compare them for size of frame and cylinder. You WILL change your mind. My mod 19 2 1/2 is half again heavier then my 4" Mod 10. The mod 10 was and is built tough, but there is a limit...

 

[Brian Williams]

Nope, dumb idea.

 

[roaddog28]

Go buy yourself a model 19/66. There is more to it than just the cylinder.

Good luck,
roaddog28

 

[BCRider]

EDITED-

I wrote up something saying this was a really bad idea and a lot of reasons why. Then I see references in Oyeboten's other thread about conversions being done. So I've edited my post to say that I'll sit back politely now and await the history lesson that I know will be coming soon.


But in the meantime I will ask one question. What about the barrel rifling? Recently I was playing with some different bullets and powder loads. My own Model 10 really seems to shine with softer loads more along the traditional target loads. But with hotter jacketed bullets the grouping seems to suffer. On the other hand my 19 doesn't care for the soft lead loads and does better groups with the jacketed ammo with hotter powder charges. Are the barrels rifled differently on these two models to better match the bullet speed ranges and types they are mostly fed? For SD work at up to 15 feet the difference won't matter. But if you enjoy target shooting the difference is highly noticable. Like jumping from 1.5 inch groupings to 4'ish inch groupings at 12'ish yards. Part of it was me mind you. I think I was getting tired. But after every more open group when I went back to an ammo I knew the gun liked things tightened back up.

 

[jad0110]

it would probably be cheaper to rechamber it to .357 than to sell it and buy a .357 K frame.

Actually, it is the other way around. Not only will you need a K Frame Magnum cylinder (they are slightly longer, and are heat treated differently to handle Magnum pressures), but you will need to have it properly fitted by a competent gunsmith who has the proper tooling to do the job. Even more problematic, .357 K-Frames have a cut on the bottom of the forcing cone because the Magnum versions require additional clearance to to accommodate the cylinder swing.

Figure $100 for a used Magnum cylinder, plus another $50 or so to fit it, plus another $50 to reshape the forcing cone, and you are looking at $200 easy. Figure an extra $50 for surprises.

So that's $250 for the mods. And I'm not a gunsmith, there may be other things I'm leaving out.

OTH, you could sell your 10-7 for around $275, assuming decent condition (+/-$25). So for $275 plus the $250 or so you would have sunk into converting it to .357 Magnum, you would have over $500 cash in your pocket for a K Frame Magnum.

Though they've increased in price, you should be able to find a nice 4" 357 Model 13, 19, 65 or 66 for under $500, pinned & recessed if you prefer.

Then again, I wouldn't sell that fine 10-7 if I were in your shoes. I'd just bite the bullet and save up for a 357.

 

[John Wayne]

Before you do it. Next time you happen to run across a S&W mod 19. Compare them for size of frame and cylinder. You WILL change your mind. My mod 19 2 1/2 is half again heavier then my 4" Mod 10. The mod 10 was and is built tough, but there is a limit...

I have not taken steps toward doing it, I just wanted to know if it was possible.

Nope, dumb idea.

Gee Brian, thanks for the constructive help and heartfelt response.

Go buy yourself a model 19/66. There is more to it than just the cylinder.

If I could buy a model 13, 19, 65, or 66, I would have no desire to have my 10 rechambered. Just wanted to know if this was an option.

No manufacturer advocates caliber conversions, but people do it to Rugers all the time, and no one says that's a "dumb idea." There are plenty of people who claim that the K-frame .38 is a strong action, so what's wrong with asking whether it can be modified to fire .357?

Many also claim that modern .38 loads and load data are not as hot as they used to be. Why is it illogical to question whether the model 10, an all-steel, medium-framed gun, might be capable of withstanding .357 given that S&W produces smaller, lighter guns chambered in this caliber?

Lots of people convert guns to fire different cartridges. There ain't exactly a manual for it, or a list of what is and isn't possible.

Also, it's a bit difficult to tell by looking at internet stats of a gun you don't have access to (i.e., model 13, 19, 65, 66) that there are areas that are beefed up or that have been heat treated differently. They weigh more, but the bull barrels and underlug vs. the 10's pencil barrel can explain that.

 

[Stophel]

It's not a stupid question, but it's definitely not a good idea. You don't know 'till you ask.

You probably couldn't find anyone who would do it anyway.

The reason that S&W came up with the L frame is that the K frame is only just barely heavy duty enough for .357, and that's with everything specifically made for it.

I've always wondered about the "heat treating" explanation. Why not make all your guns with the superior metallurgy and heat treating? Why make some inferior?

You can shoot all the +P .38's you want in the Model 10, and it will be fine. The .357, I think, will just be too much for it. Even +P .38's are incredibly low in pressure compared to full-on .357 loads.

I think that older .38 loads tended to be somewhat close to modern +P's (like 850fps or so). Then there was the .38HD load which was NOT to be used in K frames or small frame Colts, but only in the .38-44 Heavy Duty N frame. As I understand it, this spit out a bullet at about 1100 fps or more.

Your Model 10 shoots better with lead bullets because the rifling was set up for 158gr lead bullets.

Model 19's and the other K frame magnums are not hard to find at gunshows. It's a very common gun.

 

[BCRider]

Looking over my 10 and 19 side by side I'm not seeing a lot of difference between the frames themselves. In fact given that the 19 has a wide and deep channel down the top of the frame for the adjustable sight compared to two solid ridges of metal for the 10 I'd have to say that the 10 has more metal in the cross section of the top strap of the frame than the 19. And since it's the top strap that would be withstanding the brunt of the pressures this is a bit of a shocker. So as far as the frame is concerned it comes down to the alloy used for the frame and the level of heat treating done to it.

By far the biggest difference in sizing is the barrel itself. The forcing cone diameter is larger on the 19 with the little flat area. The 10's is plain round and slightly smaller. The barrel of the 19 has a much heavier wall without the taper of the pencil barrel 10.

I still don't support the concept of this but as far as the frame goes it seems to be mostly a matter of the metallurgy and heat treating. Then there's the metallurgy and treating of the cylinder.

Why not just be satisfied with shooting some +P occasionally?

 

[Oyeboten]

Hi John Wayne,



A good topic for learning and sharing and wondering.


I have suspected that the Metalurgy of the Model 13 or other comparable size or K-Frame S&W .357 Magnums, would be different from the Metalurgy of the Model 10, the Cylinder particularly.

Then, I also wondered if there was in fact any difference.

Maybe I will call S&W and see if I can find someone to talk with on this.

I have heard it said, that one does not usualy get to find meaningful suggestions of overpressure in the fired .38 Special Cartridge Casing, since the Cylinder and Topstrap blowing, are the primary indicator of having exceeded the elastic limite of the materials-components.


One sometimes sees 19th Century Revolvers with one Cylinder Chamber blown out on the side, or part of it blown out, while all else appears fine.

Of course, in an 'Open Top' design there is no Top strap to be injured in such an event.

Though far as I have seen on the internet or otherwise, contemporary misadventures in overpressure with Revolvers of any sort, tend to result in a bowed UP Top Strap, and, usually, three Cylinder Chambers opened completely.


These seem universlly respected as resulting from double charges or worse of Bullseye or maybe other 'fast' small bulk Powders.

Would a standard .357 Magnum Loading do this to a Model 10?

I am sure it would not...but, I would accept that it would subject the Revolver to more than twice it's rated capacity, as far as the Revolver's tolerence of pressure/duration of it's ostensible rating.


Proof Loads - I think - used to be of two sorts:

One) Twice the Powder, and, the Lead Ball Bullet which would be normally used.


Two) Twice the Powder, and, two of the Lead Ball Bullets which would normally be used.


How this was accomplished in Revolvers, I have no idea.

How Proof Loads are accomplished now-a-days, in Revolvers, I have no idea.

I imagine calcuations are made for using additional Powder and or possibly heavier Bullet weight as well.


If we knew the details of what S&W uses as 'Proof Loads', or, what they had used, or hired out to be used, for the Model 10, and, for the Model 13 or 19 also...we'd have at least some idea of their practical opinion as for the upper limits of pressure/duration/load which for them, in defining the 'Proof', infer lesser loadings as 'possible' to some degree or other, barring fatigue or other factors over time and repetition.

Standard Loadings for either then, would be however much below that...of course.


.38 Special 'SAAMI', I think is around 17,000 PSI

.38 Special +P, 18,500 PSI

.357 Magnum, 35,000 PSI

.38 ACP ( if memory serve, ) 26,000 PSI

.38 Super, ( if memory serve ) 34,000 PSI

9mm '08, or, 9mm Luger, 35,000 PSI



Superficially, I would expect that a conversion of an erstwhile .357 Magnum to .38 Super, or, to 9mm '08/Luger, would present no issues as for pressure/duration problems, since they are all about the same for each Cartridge.


Converting an erstwhile .38 Special Revolver to 9mm Luger, .38 Super, or, .357 Magnum, is asking an ostensible Rating to more than double in practice.


Yet, have I not heard of people converting .38 Special Revolvers to 9mm Luger, with nothing in the way of problems or regrets?


Granted, 9mm Luger is usually a ligher Bullet than .357 Magnum is, but...


Interesting...anyway...

 

[evan price]

Brian was right- dumb idea. If it took nothing more than reaming the chambers, don't you think S&W would have done that in the first place?

Before you repeat the "Constructive criticism/heartfelt response" quip, ask yourself if YOU are a better engineer than all of the folks at S&W who designed the Model 19.

Perhaps if you still feel the need, take some .38 spl brass and reload them to .357 Magnum specifications. This is how Elmer Keith got started with the Magnum concept. Let us know how long your Mod. 10 holds together. 125-grains at 1800 FPS or 158-grains at 1500 fps should be a good start.

 

[1911Tuner]

If all you want is a K-frame .357 with fixed sights and unshrouded ejector rod, find a Model 13 or Model 65. You won't have the thin, tapered barrel...but that can be arranged. Don't know why anyone would, though. It's quite the handful with full-power ammuntion with the heavy barrel.

 

[BCCL]

I'm a little confused by the idea that there is a difference in the size of the frame between a M10 and M19...a "K" frame is a "K" frame.

I'm sitting here with a 1956 M&P .38, a 1978 M15 .38 and a 1982 M66 .357 and there is absolutely no difference in the size of the frames from one gun to the next, however the M66 .357 magnum does have a slightly longer cylinder and slightly shorter forcing cone than both .38 specials.

 

[1911Tuner]

BCCL...See this post from a simliar thread.

http://www.thehighroad.org/showpost.php?p=6240164&postcount=16

 

[Shear_stress]

...a "K" frame is a "K" frame.

Not really. The .357 K-frame is reinforced around the yoke and has a different heat treatment for the cylinder.

 

[BCCL]

I had, I'm familiar with the history of the cartridge and it's "N" frame origins. I think there was some references in that thread as well about .357 "K" frames being somehow a different size than .38 "K" frames.

I've never seen any size difference in the frames from .38 t0 .357 in "K" frames?

 

[Shear_stress]

I've never seen any size difference in the frames from .38 t0 .357 in "K" frames?

See my post above. The differences are there, but subtle. You don't need to add a lot of steel to add a lot of strength.

 

[1911Tuner]

The .357 K-frame is reinforced around the yoke and has a different heat treatment for the cylinder.

While the cylinder heat treatment is a given, the yoke and crane are identical between the two, as is the material surrounding them. FWIW, I'm sitting here looking at a Model 10 and a Model 65...and aside from the cylinder lengths, the two guns are identical. Reinforcing the yoke and crane would be of no real consequence. Those parts aren't under direct stress.

BCCL...The problem isn't so much with the cylinder as it is with the frame. Pressure isn't the killer. Recoil impulse is. The frame stretches over time with attendant headspace increase. As headspace increases, the case backs up in the chamber. When it reaches a condition of insufficient head support...somethin's gonna give.

When the gun is fired, the bullet exerts a forward drag on the barrel while the recoil impulse slams the frame backward...placing the topstrap under an opposing...tensile...stress.
There are many who don't understand how topstrap stretch occurs, and will argue against it hotly...but that doesn't alter the reality.

The higher the pressure, the harder and faster the bullet is accelerated...and likewise for the recoil shield...essentially the breechblock. The topstrap is caught in the middle of this ballistic tug of war. Steel...being malleable...stretches. Also being elastic...it snaps back...but it snaps back a tiny bit less with every firing, and the stretch starts to take a set. As it slowly increases, headspace increases. The end result is inevitible.

The K-frame was engineered for lesser rounds than the .357 Magnum cartridge. It was determined that with a little different heat treating, it could be chambered for the cartridge...but the recommendation from Smith & Wesson was to limit full-powered ammunition useage in the guns. The advice was ignored for the most part...and Model 19 revolvers were being shot loose in short order. The people who realized that something was going wrong stopped with the steady diet. Those who ignored the warning signs blew up guns. Smith & Wesson threw in the towel and introduced the revolvers that split the difference between the K and N frames...the L-frame. That move was aimed directly at the shooters who wanted a smaller gun than the big N frames, but insisted on firing full-powered ammunition every time they pulled the trigger.


The more stress you place a machine under, the faster things break and wear out. Your Honda Civic will last for a couple hundred thousand miles with proper care. If you strike out on a 500-mile trip, and try to run it at redline the whole way...you probably won't get there. The Civic wasn't engineered for the Daytona 500. The K-frame Smiths weren't engineered for thousands of rounds of hot .357 ammunition. Just one of those things.

 

[BCCL]

While the cylinder heat treatment is a given, the yoke and crane are identical between the two, as is the material surrounding them. FWIW, I'm sitting here looking at a Model 10 and a Model 65...and aside from the cylinder lengths, the two guns are identical. Reinforcing the yoke and crane would be of no real consequence. Those parts aren't under direct stress.

Yep, putting the .357 in the "K" frame was the result of improved metallurgy and heat treating, not increasing the size of the frame.

 

[Shear_stress]

Yep, putting the .357 in the "K" frame was the result of improved metallurgy and heat treating, not increasing the size of the frame.

My information is from Supica and Nahas' Standard Catalog of S&W. They probably know what they're talking about. When I get back from back I'll throw on some calipers and measure the front of the frame. Again, the differences are subtle, but they are there.

Edited to add: by "yoke area" they don't mean the yoke, they mean the front of the frame.

 

[Stophel]

As I understand it, Model 19's (and the other K magnums) have problems with forcing cones cracking. Just too much for the smaller diameter barrel breech end. Is that not correct?

 

[MCgunner]

I had a forcing cone crack on my pencil barrel M10 just shooting wadcutter. I attribute it to lead build up at the forcing cone. That's how weak the K frame forcing cones are. I have a Taurus M66, actually two, that have ROUND forcing cones and beefier frames in the forcing cone area. They're fantastic shooters, same size as my K frames, and lack the weak forcing cone. I've sold the M19, but I hang on to that old M10. It was my grandpa's and ain't goin' anywhere. It now wears a heavy barrel which I actually prefer, better balance, and I keep the danged barrel/forcing cone squeaky clean now days.

 

[BCCL]

Shear Stress, My apologies, you seem to be correct.

I just got out my measuring stuff, and checked all 3 of my "K" frames, and the .357 magnum does have a little bit more steel in the front of the frame where the crane goes in.

I borrowed this picture from a website and added my (poorly drawn) green arrow to point to where I mean.



It is nearly impossible to see without a measuring device, but my M66 has just a bit more steel there, that either of my "K" frame .38 specials.

 

[John Wayne]

If it took nothing more than reaming the chambers, don't you think S&W would have done that in the first place?

Before you repeat the "Constructive criticism/heartfelt response" quip, ask yourself if YOU are a better engineer than all of the folks at S&W who designed the Model 19.

Perhaps if you still feel the need, take some .38 spl brass and reload them to .357 Magnum specifications. This is how Elmer Keith got started with the Magnum concept. Let us know how long your Mod. 10 holds together. 125-grains at 1800 FPS or 158-grains at 1500 fps should be a good start.

I don't own a K-frame .357, and I don't have any experience with them. For all I know, S&W could have just reamed out the chambers and put a heavy barrel on the gun. I am not well-versed in the history of S&W, and I am not an engineer. THAT'S WHY I ASKED.

I'm not trying to blow up a gun by hot loading .38 SPL casings. I asked if a specific modification (that I lacked information on) was possible. Saying "no, dumb idea" tells me nothing. Dumb idea could mean a lot of things, like "no, you'll ruin the value," "no, you'll blow your hand off," "no, it's not cost-effective," or "I don't really know but wanted to chime in."

Thank you to 1911 Tuner and others for actually posting useful information about why this is not possible. I now better understand the nature of the k-frame .357, and the limitations of that platform.

 

[Brian Williams]

Sorry, I apologize for not providing more information, I was headed for bed and I wanted to just let it be known that this was a Dumb Idea.

Quote:
Nope, dumb idea.
Gee Brian, thanks for the constructive help and heartfelt response.

If you want constructive help, talk about new grips or smoothing a serrated trigger, If you want heartfelt responses, don't talk about buggering up a good handgun by trying to put a cartridge in it that it was not built for.


My mercy quotient is very low for someone purposefully trying to do something that could cause a problem either with a another person, themselves or a piece of hardware/equipment.

If you have an accident or you are sick or harmed by fateful incidents, I will have buckets and bundles of heartfelt responses.

I have built or had built guns that have powerful cartridges for the frame they are in but I called S&W and checked. I also have a S&W 65(357) with a model 64 standard tapered barrel(38) on it and I called S&W and they said not a problem, but they wont do it.

Some people think that boring the chambers of an N frame Heavy Duty to 357 is to much, but that is just something that ruins the value of the gun.