Cyl throat vs barrel

[Gatch]

Why is cylinder throat as opposed to barrel bore the more relevant measurement when it comes to casting for revolvers ? Or have I gotten this mixed up ?

I ask because I'm mulling over the idea of getting a .357mag for fun. Bowling pin, silhouette, icore and steel challenge stuff etc. It also means no extra work to maintain my license and I can share boolits between 357 and 9mm.

Your wisdoms would be appreciated.

[sigep1764]

Its proper that the cylinder throats be just a little bigger than bore diameter to let a boolit sized 2 thousandths over bore diameter enter the bore. If you sized to bore diameter and the cylinder throats were bigger than bore diameter, you would lead the cylinder throats and more than likely lead the bore. If the cylinder throats are smaller than bore diameter, you would be shooting lead boolits that will surely enter the bore under bore diameter leading to leading.

[DougGuy]

Because in many instances, the boolit will exit the front of the cylinder at throat diameter, regardless of what it was sized to when loaded. If throats are .356" and you load a .358" boolit it will still be .356" when it is fired through the tight throat.

In a perfect world, the boolit would be .001" to .002" greater than groove diameter, cylinder throats would be .0005" to .001" greater than boolit diameter. This works for any centerfire revolver, regardless of caliber.

[Outpost75]

Read the sticky.

And a bullet 0.002 over bore diameter would be waaaay to small to fill the grooves. Bore diameter is the size of the drilled and reamed smooth hole BEFORE the barrel is rifled and represents the diameter across the tops of the rifling lands.

0.002" over groove diameter in a .357 would be larger than the cylinder throats of many revolvers as they come from the factory.

Don't worry about measuring barrel groove diameter, measure cylinder throats and size bullets to fit.

If cylinder throats are not uniform or are smaller than barrel groove, they can be reamed or honed to correct size. DougGuy does mine.

[Piedmont]

Gatch, Here is another point to consider. You want to control a straight alignment of your projectile as much as possible so it will fly more accurately. If your cylinder throats were larger than your groove diameter, which is a very common situation, and you sized for the groove diameter, your bullet could get a little cattywhumpus in the cylinder throat and wouldn't shoot consistently with the subsequent bullets that also were cattywhumpus but to different degrees and angles. If the bullet was hugged by the side of the cylinder hole all the way around it couldn't tip and then when it hit the forcing cone of the barrel it would be headed straight ahead going into the barrel and straight ahead coming out of the barrel. Then the boolits would hit the paper closer together.

[mehavey]

Why is cylinder throat as opposed to barrel bore the more relevant
measurement when it comes to casting for revolvers ? Neither is "more" relevant. They both need to be matched . . . with the cylinder just a skosh over groove diameter . . . and the bullet sized "just a skosh" over that again.

This is why -- in modern 45 Colts (especially Rugers) -- Brownells is doing a bang-up business in 0.4525" throat reamers.
https://www.brownells.com/gunsmith-tools-supplies/barrel-tools/reamers/throating-reamers/revolver-cylinder-throating-reamer-prod7700.aspx

[Gatch]

Because in many instances, the boolit will exit the front of the cylinder at throat diameter, regardless of what it was sized to when loaded. If throats are .356" and you load a .358" boolit it will still be .356" when it is fired through the tight throat.

In a perfect world, the boolit would be .001" to .002" greater than groove diameter, cylinder throats would be .0005" to .001" greater than boolit diameter. This works for any centerfire revolver, regardless of caliber.

Perfect thanks mate.

[DougGuy]

Neither is "more" relevant. They both need to be matched . . . with the cylinder just a skosh over groove diameter . . . and the bullet sized "just a skosh" over that again.

Are you suggesting to size the boolit larger than the throat?


This is why -- in modern 45 Colts (especially Rugers) -- Brownells is doing a bang-up business in 0.4525" throat reamers.

Reaming cylinder throats is one thing, you still have to clean up the ridges and tool marks left by the reamer, AND if that cylinder has any variation in hardness from one side to the other, which a LOT do, you will have different sized throats even after reaming and now you are right back at the uneven dimensions that Ruger ships many of them with. The softer and easier the throats cut, the larger the reamer will cut them. If the cylinder is hard, or harder on one side than the other, it will cut smaller in the harder metal than it will in the softer metal. You basically are at the mercy of the metallurgy of that specific cylinder, how good of a job the reamer will do and how even it will cut. Or not. This is why I use the Sunnen hone, it is stepless and can size throats to consistency regardless of the metallurgical makeup of the cylinder. A reamer CANNOT do this. Maybe in S&W cylinders where they are all softer and machine easier than Ruger, but not in many Ruger cylinders.

[40-82 hiker]

I just sent another cylinder off to DougGuy. He knows his stuff. I would suggest you get in touch with Doug when you get your .357, but I sure don't know about the shipping from Brisbane!

Ideally, you would want to pass a boolit through the throat of the cylinder chamber with but a little finger pressure (want a little drag so the boolit does not simply drop through). However, larger than throat diameter is not really the place to be. At least that has been my experience, especially after being tutored on CB pages by Doug and others.

[tazman]

Being over throat size by a thousandth or two isn't dangerous, but it isn't a good idea. Accuracy suffers as a rule. You don't know if the boolit is getting sized down in a perfectly balanced manner.
Ideally, you would have a sliding or light pressure fit of the boolit to the throats. At this point the boolit needs to be at least as big as the groove diameter of the barrel,preferably, 1 to 2 thousandths larger.
I have a revolver that has a small for caliber groove diameter and small throats. Fortunately the throats are slightly larger than groove diameter. I still shoot my standard ammo in this revolver, but the accuracy isn't optimal. It is adequate for the usage of the gun(S&W 60 in 38 special with 3 inch barrel)
All my other revolvers are sized what you would expect for 38/357 caliber guns and work well with standard sizing.

[Gatch]

Are you suggesting to size the boolit larger than the throat?



Reaming cylinder throats is one thing, you still have to clean up the ridges and tool marks left by the reamer, AND if that cylinder has any variation in hardness from one side to the other, which a LOT do, you will have different sized throats even after reaming and now you are right back at the uneven dimensions that Ruger ships many of them with. The softer and easier the throats cut, the larger the reamer will cut them. If the cylinder is hard, or harder on one side than the other, it will cut smaller in the harder metal than it will in the softer metal. You basically are at the mercy of the metallurgy of that specific cylinder, how good of a job the reamer will do and how even it will cut. Or not. This is why I use the Sunnen hone, it is stepless and can size throats to consistency regardless of the metallurgical makeup of the cylinder. A reamer CANNOT do this. Maybe in S&W cylinders where they are all softer and machine easier than Ruger, but not in many Ruger cylinders.

I'm not a gunsmith and have never worked on tuning up guns like this. But I apprenticed in a machine shop and understand 100% what you're saying. When you spend some time machining and grinding you soon see inconsistencies in heat treatments. You would think that with all the years that people have been hardening and tempering things, a big company like ruger (and others) would be able to get it right first pop.

[Outpost75]

I'm not a gunsmith and have never worked on tuning up guns like this. But I apprenticed in a machine shop and understand 100% what you're saying. When you spend some time machining and grinding you soon see inconsistencies in heat treatments. You would think that with all the years that people have been hardening and tempering things, a big company like ruger (and others) would be able to get it right first pop.

I used to be QA manager at Ruger, Newport, NH.

The company did better than most when I was there in the 1980s, but what DougGuy says is 100% correct.

As WBR, Sr. would say, "It doesn't need to be any better than that for farm boys who are going to shoot at cans..."

[sw282]

l have read several times that KORTH revolver cylinders are made of ''TOOL'' steel. lf this is true, then what kind of ''tool'' does Korth use to cut their tool steel cylinders with:?::?:

[Gatch]

l have read several times that KORTH revolver cylinders are made of ''TOOL'' steel. lf this is true, then what kind of ''tool'' does Korth use to cut their tool steel cylinders with:?::?:

Tool steel is a pretty broad term. Most kinds of tool steel are machined the same way as any other kind of steel, ie hss or carbide tip tools. The real value of most grades of tool steel aren't realised until they are hardened and tempered and finish machined or ground to relevant size/finish.

A nicely tempered and ground piece of 4340 (high tensile) will out perform an untreated piece of almost anything etc.

[243winxb]

share boolits between 357 and 9mm. Not if you want optimum accuracy in both. Jacketed yes. Lead no.

All will make it out the end of the barrel.

The early Lyman cast bullet manual said to size bullets to groove diameter for handguns. Been doing it that way for many years.

Alloy, Lyman #2 hard. BHN 15.

[Outpost75]

l have read several times that KORTH revolver cylinders are made of ''TOOL'' steel. lf this is true, then what kind of ''tool'' does Korth use to cut their tool steel cylinders with:?::?:

Can't speak to Korth, but when I was at Ruger cylinder blanks for blued guns were made from 4140 chrome-molybdenum steel at a Rockwell C hardness of 28-32. The cutting tools were much as Gatch describes, alloys and cutting fluids would vary by application. Most tools were either TiCN coated tool steel, with carbide used for core drills, roughers, semi-finishers, specifics depending upon the operation. Physical properties of stainess cylinders and tooling used were similar, using vacuum melted, argon-oxygen decarburized and ladle refined material of proprietary composition, purchases in 100-ton heat lots, cropped and rolled to our specification. The specific material requirements would be familiar to those in the nuclear power industry.