Slugged my K-38

[Cosmic_Charlie]

Getting nice groups with .358 tumble lubed soup can boolits but also a bit of leading. So I slugged the barrel. These Smiths have an odd number of grooves so measuring the slug is not easy. But since it's a revolver I tried the slug in the cylinder throats and it was a very tight fit. My .358 boolits won't easily push through the throats either so I figure the throats are really close to the groove diameter.

I could powder coat my boolits and size them to .358 or i could have the throats reamed to .3585. I like the idea of shooting lubed boolits with no leading as opposed to powder coating but this revolver is a real beauty and I'd hate for something to go sideways if i sent the cylinder off for work. Got a Super Blackhawk and a 24-3 that can shoot lubed with no leading.

[Outpost75]

Cylinder throat fit is more important than barrel groove diameter.

Fit bullets to cylinder throat - 0.0005" so they are a sliding push fit with slight resistance with hand pressure only.

[Der Gebirgsjager]

Have you ever tried any .357 diameter bullets?

[Misery-Whip]

I had one for a spell. It too liked a swc soupcan with alox. But loved the 105swc by lee sized 358, aloxed and set over 3.0 bullseye. Stacked them into a ragged hole at 60'.

Powdercoated both boolits and was getting 3-4" with same load/distance.

[lotech]

Bullets just under .357" shoot better in my K-38 than .358" bullets do.

[USSR]

DougGuy on this site is who you want to contact. He hones cylinder throats and is very good at it. Very reasonably priced and fast service (about 1 week).

Don

[Cosmic_Charlie]

Have you ever tried any .357 diameter bullets?

Yes, they lead a bit more than the .358".

[MT Gianni]

To mike S&W barrels wrap the slug with non overlapping soda can tin and measure. Then measure the thickness of the wrap, double it and subtract.

[megasupermagnum]

I would try a soft alloy, something like 30-1.

[murf205]

I think you have already solved your problem when you said you could have the cyl throats reamed to .3585. Dougguy’s reputation is stellar and the results speak for themselves. Remember that most S&W revolvers have cylinder throats designed for jacketed rounds. What a shame! You

[Cosmic_Charlie]

I would try a soft alloy, something like 30-1.

I was using half coww, half pure plus tin. My old S prefix 27-2 also has throats close to groove diameter. With powder coated .358 boolits it does well. I would have more latitude with larger throats in terms of velocity. I'll mix up a batch of 30/1 and try it. Obturation may solve it.

[Cosmic_Charlie]

I think you have already solved your problem when you said you could have the cyl throats reamed to .3585. Dougguy’s reputation is stellar and the results speak for themselves. Remember that most S&W revolvers have cylinder throats designed for jacketed rounds. What a shame! You

Yep. 20 years ago when I was at the top of my game I could make some amazing shots with my 27-2 and jacketed bullets. But jacketed bullets do not interest me any longer. And the only way I can shoot warmer cast loads is with larger throats. So I may keep the K-38 as is and have the 27 done by Doug.

[Groo]

Groo here
What load? What size boolet? Crimp? More info please!!!!!!!!!!!!!!!
The last thing to do is "change" the gun...
The charge maybe too "light" for the hardness of the bullet....[not sealing well]
This will cause leading due to gass blowby [base not sealing]

[Drm50]

Yes last thing I would do is have cylinders reamed. I’ve got 3 k38s all older guns with pinned barrels, one NIB. Both shooters are tuned with Lyman button nose WCs. I’m casting 20:1 and sizing .357”. I’m shooting in 700fps range. I’ve got several k22s and m34. They are also older guns. They can be PIA to extract but I would never have the cylinders reamed or honed on them either. I’m 70 I ain’t a contender no more. I’ve seen around the ranges no matter what the game the first thing guys want to do is blame the gun. Number two, is shooter capable of benefiting from the degree of accuracy obtained by any adjustments.

[Cosmic_Charlie]

Yes, softer may be better. I have both 20/1 and 30/1 left over from when I first started casting ( Roto Metals). My K-38 is a 1956 vintage 4" that was all but new. 3.2 grains of bullseye under a 148 grain tumble lube soup can. Slight crimp in the first groove. Alloy was half coww, half pure with some tin. BLL lube. I will let you know how softer goes.

[Larry Gibson]

"Getting nice groups with .358 tumble lubed soup can boolits but also a bit of leading."

I've no doubt that K-38 S&W barrel has a .357 groove diameter at the largest. Thus .357 sized bullets in .357 throats is about as perfect a fit as you'll get. No, in a revolver you do not need larger diameter bullets than groove diameter if the throats and sized bullets are the same diameter. The 4 most accurate revolvers I've had [38 SPL Power PPC on a M10 S&W, 5" M15 S&W 38 SPL, Ruger Bisley 41 Magnum and a Colt Anaconda 44 Magnum] all have throats the same diameter as the barrel groove diameter.

I would never even consider enlarging the cylinder throats [no disrespect for Doug or the work he does intended] if the revolver is "getting nice groups". What little leading you're getting is a lube issue not a "sizing" issue. I'm not "into" PC but have tested enough to answer why I'm not "into" PC so won't comment there. The TL you're using isn't working well enough or perhaps the applications isn't correct? What TL lube are you using?

[DougGuy]

I would never even consider enlarging the cylinder throats [no disrespect for Doug or the work he does intended] if the revolver is "getting nice groups".

What you are ultimately after, is the "seal" that the boolit achieves in the bore. About the only time using a boolit exactly the same size as groove diameter becomes detrimental is when and if the boolit doesn't seal as well as it needs to in the bore. If it gets launched a tad bit eccentric, it may engrave the rifling deeper on one side than the other which leaves one side loose enough to pass gas by the boolit, and also to throw the boolit into a spiral when it leaves the muzzle instead of a spin. For THIS reason, I usually always recommend the boolit .001" to .002" greater than groove diameter, and the throats of course .0005" to .001" greater than boolit diameter.

The back side of the above arrangement, is that A. if you have throats .0005" bigger than groove, then B. when you fire a soft enough alloy over a stout enough charge, you do seal to the throats with obturation, and now you are presenting a slightly greater boolit diameter to the bore. In other words size a soft boolit to .357" it leves the throats at .358" or .3585" or whatever the throat diameter is. In this manner you are improving the chances of getting a good seal in the bore because there is a bit of boolit to swage into the rifling. IF this is the case, then you may see groups improve over sizing a harder boolit to the existing throat diameter, or half thou smaller. Which is why sizing the throats to .3585" and using .358" boolits works as well as it does. Again, it is the SEAL in the bore that is the key to good groups. That and how concentric the boolit is when it engraves.

[USSR]

...when you fire a soft enough alloy over a stout enough charge, you do seal to the throats with obturation, and now you are presenting a slightly greater boolit diameter to the bore.

This is why commercially cast bullets sometimes lead; for the commercial casters 12 BHN is considered "soft" and you don't get the obturation.

Don

[Cosmic_Charlie]

I got no complaints with the accuracy of any of my Smiths. Just don't like the leading. And it's pretty minor too. I will try the softer alloy and perhaps a bit more lube. Will also try the boolits sized to .357 again. Thanks for all the input guys.

[DougGuy]

Yes last thing I would do is have cylinders reamed. I’ve got several k22s and m34. They can be PIA to extract but I would never have the cylinders reamed or honed on them either.

They tell me there are two kinds of shooters at the kit gun matches, ones who have had their cylinders reamed, and ones who are planning to have their cylinders reamed.

Why does it come down to yoking one's self to working with a mechanical object that is not to the optimum that it could be? I don't understand the logic in that at all. A revolver, any revolver, in a perfect world, has dimensions that read not unlike a common kitchen funnel. Larger dimensions in the back and getting progressively smaller as you go forward. No constrictions, no tight throats, just a uniform progression that keeps the boolit sealed and snugly guided as it travels. It's a no brainer that THIS arrangement is mathematically and ballistically MUCH better than a randomly chosen and assembled piece of machinery whose parts and components may or may not be very well matched, and you basically get what you get and that's that.

FIT the boolit to the barrel. OH! But the cylinder prevents that! Well, the cylinder is now a multi-port sizing die, and it could be greatly improved on to the satisfaction of the owner, AND to the accuracy of the pistol itself.

I have reamed a LOT of K guns, they are no longer finicky with ammo brands, and they drop the empty brass out with very little or no effort other than tilting the muzzle skyward and swinging the cylinder out of the frame. I have not had ONE COMPLAINT yet. But to each his own. If you want to shoot a gun that frustrates you every time you go to unload it, or every time you have to clean the barrel or the cylinder, or you just wonder if it could shoot better, go ahead, that's certainly your choice to make.

There are gains to be had when things are fitted correctly, just be very thankful that they didn't grab a one size fits all reamer and now you just WISH cylinders would be made smaller, tighter, etc...

[Drm50]

I got several S&Ws and only leading I ever had was with Speer 45 SWC. I was shooting at 700fps with Unique. Worst leading I have ever seen. Out of 25-5, 83/8” the lead was working out of muzzle by 18th shot. Looked like Elmer Fudd cartoon but lead came out easy with just bronze brush.

[murf205]

This is why commercially cast bullets sometimes lead; for the commercial casters 12 BHN is considered "soft" and you don't get the obturation.

Don

That, and the fact that a lot of commercial casters use beveled base molds to facilitate easy drop out of the mold. Almost all the leading I've experienced is from bb boolits. It is kinda like inviting the gas up onto the base.
The reason I recommend cylinder reaming AFTER everything else has been tried is because it worked...for me in 2 instances. I have a M24 Smith&Wesson that had .429 throats and a couple that were .4285 and it leaded in spite of trying 3 different lubes and about 6 differrent powders. I drove 429421's fast, slow, and medium but the lead was still there, not to the point of unshootable but still there. The barrel is a EDM rifled barrel and it looks like a mirror. I have a 44 Hand Ejector made in 1926 that has .432 throats and it is the most accurate 44 I own, so I reamed the throats to .431 and it changed the game instantly.268698These targets are what I finaally got the Model 24 to do. It is not a match grade gun but it does not lead anymore.

[catboat]

It has not been mentioned yet. You may have an issue of thread choke. The bore /groove diameter inside the frame (throat) may be squeezed down 0.001-0.002", as the threaded barrel is tighter in the frame. If thread choke is present, a bullet is sized down to that choked down (reduced) bore/ groove diameter, and obviously stays in that reduced diameter as it goes down the barrel. This reduces accuracy, and causes leading ( at the throat (shear) and/ or in the barrel ( gas blow by).

You can determine if you have thread choke by slugging the bore ( from the muzzle) and using a few cast bullets. Lube the bore, and push one bullet in an inch or two, then tap it out back to the muzzle.

Make a couple cut off dowel pieces that just fit inside the frame, and put them in from the throat side. Depending on barrel length, you will need 3-4 dowel piece about cylinder length length, and one dowel piece about 1/2 cylinder length. The "1/2 cylinder length" dowel piece is used to allow enough space behind the dowel to permit you to place something hard behind it to apply force toward the muzzle to remove the slug.

Measure the slug (even if it has 5 grooves).

Repeat, making a slug down another 1-2". Remove from muzzle end. Measure.

Then push a slug from the muzzle through the throat, and catch it. Measure.

If the pushed-through slug is smaller diameter than the other slugs ( which did not pass through the throat), then you have "thread choke." It needs to be removed for best accuracy.

Two ways to correct for thread choke: fire lapping, or having the barrel modified to a "Taylor throat." ( reamed /tapered throat. Both remove the tight spot in the barrel, and usually improves accuracy, and reduces leading.

Then check cylinder throat diameters. They should all be uniformly the same diameter, and about 0.001" larger than the barrel's groove diameter (without thread choke restriction). You may need to have the throats reamed open ( not opened with an abrasive strip on a dowel , chucked into a drill. This creates an oval-shaled, non-parallel cylinder throat which is less-than-ideal for best accuracy).

Repeating the concept and strategy: The proper diameter bullet will then just fit through the cylinder throats, with just a bit of force ( ie, you can push the bullet through each cylinder throat with a dowel or pencil.). The bullets should not fall through the cylinder throats with just gravity. You want the cylinder throats about 0.001" larger than the "thread choke less" groove diameter.

There are multiple areas to measure, and possibly correct for getting the most out of your revolver. The solution is likely not just changing bullet diameter itself.

[Cosmic_Charlie]

This is a 1956 vintage gun with a pinned barrel so I doubt thread choke is the issue. Plus I felt nothing as the bullet approached the forcing cone. And it shoots nice groups. I just don't like the leading even as minor as it is.

[murf205]

What part of powder coating do you not like, the process or the colors? Smoke sell a clear powder that looks like, well, clear. It might just be worth your time to try some pc'd boolits just to see.

[catboat]

Do your bullets ( not loaded cartridge) fall through the cylinder throats, or do the need a push with a pencil? I seem to remember reading that some s&w model 25 had large throats ( .454"++). If you are shooting a .451-.452" lead bullet, you will likely get gas blow by, and create leading.

Use a pin gauge, or place a lead slug in each cylinder, tap it to expand a bit, then push a different bullet through each throat and get the slug's diameter for each throat. You obviously want the slug bigger than the throat before you tap it through, so the slug will be sized to the throat diameter for accurate dimensions .

[USSR]

I seem to remember reading that some s&w model 25 had large throats ( .454"++).

Actually, it is MOST of the Model 25's, until they dropped the pinned barrels.

Don

[Cosmic_Charlie]

What part of powder coating do you not like, the process or the colors? Smoke sell a clear powder that looks like, well, clear. It might just be worth your time to try some pc'd boolits just to see.

Mostly just the extra time involved verses tumble lube. I figure if I can shoot 1650 fps tumble lubed boolits without leading in my .308 I ought to be able to do it at 800 fps in my revolver. I powder coat my 9mm boolits.

[DougGuy]

My .358 boolits won't easily push through the throats either so I figure the throats are really close to the groove diameter.

If a boolit won't push through the throats without force, then the cylinder is at this particular moment in time, a multi port sizing die. So it's either sizing to the groove IF the throats are indeed the same size as groove diameter, or slightly smaller than groove. Just sounds like not quite enough boolit to swage into the rifling enough to make a good seal.

[Cosmic_Charlie]

Well it is curious. My 24-3 shoots .432" boolits because it has large throats. Have not bothered slugging it because it is accurate and does not lead. My Super Blackhawk uses .431 and also is trouble free. My Model 60 Pro likes .358 boolits. But my two oldest Smith's have very tight geometry. Thanks for all the input fellas. Now I get to try a few things.

[Cosmic_Charlie]

Powder coated .357 boolits did the trick. I also tried some 16/1 alloy for the .357 and 8.7 HS 6 but have not shot them yet.