best way open up cylinders to .358 for lead ?

What is the best way to open up cylinders to .358 for revolvers that will only ever shoot plain lead ?
The Cast boolit forum suggests this to help reduce leading from minimal to zero.
I purchased a used 686 cylinder to practice on and used a letter T reamer to make the cut.
Technically it worked ok and the cylinder throats are opened up to about .3585 now after some polishing and functionality is good.
The finish from the reamer isn't so great, A bit embarrassing really.
I did another test today on a grade 5 bolt to see if I could get a better finish using back gear and dark cutting oil at very slow speed.
Same result, technically the size is correct, but the finish isn't what I would like to see.
I'm a bit leary about using a flex hone to make it pretty.
How do the pros handle it ?

Why in the world wou you do that?

Spend the money on practice ammo and use it.

What is the current diameter of the throats? You can always order .357 diameter bullets. With no fear of screwing up a good gun.

What kind of reamer are you using?
Are you using a piloted reamer such as this one from Brownells?

REVOLVER CYLINDER THROATING REAMER | Brownells

If you are, and are having troubles, give Brownell's a phone call. They have excellent gunsmiths on call that can help.

Best regards,
Jim

PS: anyone else puzzled by the OP should have a look at the link, too!

The cylinder throats on all the guns I have checked measure .3575
It's a fairly common mod for cast boolit shooters.
It is a cast bullet scenario for firearms that will only shoot lead
I cast and size to .358 to fill out to the lands completely.
This greatly reduces leading, however a .3575 cylinder throat is resizing my .358 boolit. Best results are from having the bullet stay .358 all the way to the barrel.
I'm not damaging a fine firearm, the one or two I plan to make the change to are well loved shooter grade guns that will only shoot lead for the rest of their existence.

I am using a straight flute letter T chucking reamer.
Chucking the cylinder in the lathe and dialing in on a pin.
I started out life a machinist, this is typical machine shop stuff and is no different than something that would be rebranded by Brownells.
I'm not looking for a chamber reamer, that would be a specialty item from Clymer or such.

Depending on the diameter of your barrel...

... a typical .38/.357 barrel is about perfect for a .358" lead bullet because the lead is squeezed tightly in the barrel and avoids flame cutting. I just wonder why a .358" barrel would be better for a lead bullet? If I messed with honing down my barrel or 'fire lapping' or any such thing I'd have to have a REALLY good reason.

I'm not talking about changing the diameter of the barrel

To get the best finish with a reamer, run it slow and flood it with lots of lubricant. With an adjustable reamer, take light cuts rather than trying to remove all the material at once. We used to have a product called Tap Magic, that was meant to use when tapping, but it would provide very smooth results when reaming too. Unfortunately, it contained stuff that was environmentally unfriendly, so the formula was changed.

I would not do this....nor do I see any gain from it...I have nearly 20 S&W revolvers and they all shoot lead only and I don't experience excessive leading using my .358 cast bullets in any of them.....

If that is your concern run them through a .357 sizer and all is good to go. Much cheaper solution, and you are not changing anything in a valuable cylinder.

Randy

varmint243,

Before you do anything slug the barrel! This isn't to measure he slug, but to make a direct comparison between the groove diameter and the cylinder throats. If a barrel slug passes through the throats with little or no resistance you are not going to gain anything by opening the throats! Only if the slug will not pass through the throats, or with quite a bit of pressure, is there any need to open the throats.

It sounds to me like you are guessing/assuming that you need .358 bullets and don't really know what the relationship is between the cylinder throats and the groove diameter! You're getting "the cart before the horse"!

If the slug passes easily through the throats then you can't improve anything by enlarging them! If so then size to throat diameter to +.001.

It looks like I'm getting some good sugestions today from people that understand what I am trying to accomplish.
After yesterday's comments I was starting to feel sorry that I ever asked the question.
To be fair, I never did slug the bore to see what grove to grove measured.
I also thought of using a fired case to make a sleeve to protect the chambers and going from that end.
I assumed that using a lathe in super slow back gear would be better than trying to hand ream.
Brownells setup is for hand reaming, doesn't seem like the best approach to me.
I bought 2 extra 686 cylinders so i'm not put out about making a mess out of one.
I'd rather not scrap the second one.
I'm currently testing on grade 5 bolts to try to get a good quality steel for testing.
I haven't a clue how it compares to the steel a barrel is made from, barrel steel seems pretty soft to me.
I'm using some top notch dark cutting oil for lube now.
I am also assuming that stainless steel in barrels is some version of 400 series.
I may also take the second cylinder to the race shop and do it on the Sunnen wet hone.
Seems like a lot of trouble, but I could get .0001 accuracy and a good finish after I make a fixture to hold the cylinder.

With 5 land & 5 groove rifling, measuring groove diameter is going to be interesting as a land opposes each groove.

That said, you're assuming that your bore is 0.358 inches. The acceptable range of .357/.38 barrel groove diameters is 0.356 to 0.358 inches. It doesn't mean that your barrel is automatically any specific size.

Above all, you may want to experiment with different bullet diameters to determine which delivers the best accuracy in your particular gun. Assumptions that X specific diameter is going to be best can lead to expensive/extensive work with worse accuracy at the end of it.

You must have a lot of time on your hands to worry about a half mil.

>>>You must have a lot of time on your hands to worry about a half mil<<<
half a thousandth actually

It's a project
I bought a very nice condition used 686 pro series and tried to get reliable offhand groups at 40 yards with it.
To be fair I like 6" heavy barrel revolvers and never liked the darn thing since the day I took it home.
I seriously tried for about 6 moths to get it to shoot like some of my other revolvers at 40 yards.
Me and the gun just don't like each other
So I'm snowed in one weekend this winter and find a used PPC barrel on eBay that might fit it with some work.
Out of boredom, I screwed the old barrel off and this one on just to see how it indexed and what the cylinder gap looked like.
Hmmm... looks like magically it fits ok.
Take it to the range with my cast boolits.
I'm starting to get the results I might expect.
I get my lead levels tested, decided it's a good idea to stop casting for a while.
Buy some swaged HBWC, had good luck with these in other guns.
Nothing doing, leaded up like crazy FML.
Hmm, I wonder if opening up the cylinders would help.
I don't feel like messing up my nice 7 shot moon clip pro series cylinder so...
Another rainy day on eBay and I have a 6 shot 686 cylinder
Try my hand a reaming it and works ok except of the ugly tool marks.
Another rainy day, I wonder what will happen if I stick a 6 shot cylinder on the 686 pro series, I didn't like the 7 shot that much anyway.
Magically, it fits and seems to time up and function well, would have bet money against it working at all.
Hmm, time for a range trip.
Shoots ok, but I'm switching back to my own cast boolits because I can't stand the HBWC. too bad because I've only used 1k of the 2k I bought.
Seems like it might shoot again, now I'm annoyed because the reaming looks a little ratty.
So, I ordered another 6 shot 686 cylinder from the guy I got the last one from.
Now I have two choices for the next one, open it up, or run it as is.

As you might expect most of the guys I shoot with think I have a screw loose for messing with this what once was a nice gun.
At some point I actually decided to stick it in the back of the safe and bought a 586 no dash, very nice shooter grade to replace it with. I still haven't shot that gun. It has the red ramp and I prefer the partridge.

so, I could pull one of my three model 14's or my 686, or my 625 45cp that already shoot like I would expect, or I can keep screwing with the pro series until it's totally hosed.

Smart money would be putting it back to it's original configuration and selling it on here to someone who would probably really like to have that specific model. Naaa... that makes too much sense.

So, I have a little extra time and a little extra money because
don't drink, don't smoke, don't do recreational substances, don't have a wife or GF, and have already looked at all the porn on the internet.

Have you pulled a swaged HBWC after making a cartridge to check if the bullet was still .358"? I ask because I had problems with swaged bullets being sized down by brass. For 45ACP I ended up using a custom expander and a sizing die from another cartridge to keep my swaged target bullets close to their original size. I'm going through the whole process again to load for a M52.

It's your gun and your time.......so do what you want. BUT, I wouldn't mess with cylinder throat diameters until I exhausted all the possibilities with bullet diameters, hardness and bullet lubes.........

With one maybe two exceptions; I would do a basic lap of the barrel and check the muzzle crown very carefully to see if a new crown job is required. ............

You're shooting offhand at 40 yds and worrying about half a
thousandth in the chamber throat of your revolver. You have extra time,
extra money, no expensive bad habits, no wife or GF. What you do
have is displaced anxiety in my opinion. Maybe counseling can help
you focus on the real circumstances of your life that are the source of
your frustration and you can stop worring about insignificant details
of your revolvers.

Despite the naysayers, best accuracy in a revolver is always achieved with the cylinder throat diameters anywhere from 0.0005" to roughly 0.0015" larger than the barrel groove diameter. Sometimes, even a bit more. However, you do NOT want big, sloppy throats. That will lead to the bullets yawing in the throats and entering the forcing cone "out of kilter" (with obvious negative effect on accuracy). So, do go easy.

You do NOT want the cylinder throats ever to swage down the bullets. One, it wastes energy, reduces velocity and increases the rate of wear. Two, it never improves accuracy....and usually hurts it. This is true with jacketed bullets, as well as cast.

Rugers tend to be very bad on this score. For some reason, Ruger does not seem to understand this concept.....because their cylinder throats are very commonly undersized. Smith & Wessons tend, in my experience, to be much more correct. I've never had one, for example, that had undersized throats. But, that is only my experience.

So, it is NOT crazy to correct this issue, when it occurs. It is NOT a case of "messing up" the revolver. It is, in fact, correct practice. Many people are ignorant of this issue, though.

As for cleaning up the already cut throats, as long as they've been cut correctly (concentric with the chambers), then it is not necessary to use a pilot to polish them. A suitably sized brass rod, or even a wood dowel, coated with polishing paste, can be used. Almost anything, but I wouldn't use anything made of steel. So, you can improvise on this step. Even 2000 grit sandpaper, wrapped around a dowel (and used wet or with polishing paste) can be used. Just be delicate with the polishing. Polish - don't remove more material.

The cut throats almost always need a bit of polishing, so that is not unusual. I would suspect, though, that your reamer may be a bit dull.

shooting, casting, and tinkering is my stress relief (counselor if you prefer)
The old timers at the club I shoot with are a lot like my neighborhood bartender
and.... I guess the lead levels compensate for some substance abuse
It amazes me how rude people are on the forums to someone they have never met and know almost nothing about.
Why don't you come out to the club and shoot with me a few times before you make some rude comments.

It's not the insignificant detail in the revolver that bothers me.
It's the rather significant difference in the results at the target with various combinations.
A certain amount of leading has a rather noticeable impact at the target end of things.

Rowlf,
I do like the suggestion of pulling one of the HBWC to see if I am sizing it down. The lead in the swaged bullet is very soft and perhaps far more susceptible to being sized down during the cartridge assembly process.

alwslate said:

You're shooting offhand at 40 yds and worrying about half a
thousandth in the chamber throat of your revolver. You have extra time,
extra money, no expensive bad habits, no wife or GF. What you do
have is displaced anxiety in my opinion. Maybe counseling can help
you focus on the real circumstances of your life that are the source of
your frustration and you can stop worring about insignificant details
of your revolvers.

Click to expand...

Sticking to the purely mechanical......if you specified where in the barrel it was leading, I missed it. In addition to checking groove diameter, I'd take a look at the forcing cone.

I frankly don't believe the torque of most pistol barrel installations will distort the barrel to the point of affecting diameter. Given the relative thickness of barrel and frame, I'd expect the frame to expand slightly.

Finally, you mention you bought a used barrel. It may well have been for sale because it would accumulate lead for whatever reason. Decades ago, I toured the Douglas barrel plant. It was strongly suggested that the bullets pass through the barrel in the same direction the rifling button passed. When I cut pistol barrel blanks from a full size blank I took care to mark either/both muzzle or rear of each piece as it came from the lathe. Never had anyone complain about leading.