How to open up cylinder throats?

[Oreo]

So I have this new to me S&W 629-4 Mountain Gun. (44mag) I was just making impact slugs of the bore, forcing cone, and all six cylinder throats. Turns out all six cylinder throats are right at .4287", and the bore is .430"ish (5 grooves make precise measurement difficult)

So I guess that means I need to have the cylinder throats opened up to, what, .4310"? Can I buy a tool and do that myself or does it have to be done on heavy machine equipment by a smith?

Thanks for the help in advance.

[jmort]

"Can I buy a tool and do that myself..."

Yes, reamers from Brownells
http://www.brownells.com/gunsmith-tools-supplies/barrel-blanks-tools/reamers/throating-reamers/revolver-cylinder-throating-reamer-prod7700.aspx

[paul h]

You could lap the throats out, but lapping is a very slow process and best for removing tenths of a thousandth, not several thousandths. The ideal way would be to use a 0.431" throat reamer and then polish the throats with a lap and bring them to 0.4315". Throat reamers can be carefully hand turned.

[prs]

If you have pistol smith, then pay him/her to do the job. The tools and supplies are prolly right there in her/his kit ready for use and an experienced hand ready to serve. If you are diehard diy, then get the proper reamer, guide(s), handle, and cutting oil.

Did you try the pistol as is?

prs

[nicholst55]

Contact Cylindersmith.com. He may only be doing .45s these days, but perhaps he can recommend someone to do your .44 if he isn't doing them. His charge and turnaround time make buying the reamer to do one gun counterproductive.

[Oreo]

I have not tried the gun as-is. I've not fired it yet at all. Still, conventional wisdom says I've got the ingredients for trouble so I want the gun made dimensionally correct.

What does a smith usually charge for this? looks like its $160+ to buy the reamer and pilot bushing kit.

[Petrol & Powder]

I'd shoot it first before I did something irreversible like reaming throats. It's a lot easier to take steel off than to put it back on. The worst that can happen is some leading and that's easy to remove. You may find that it shoots fine. I've got a S&W with tight throats but it shoots great with cast bullets.

[Larry Gibson]

I'd shoot it first before I did something irreversible like reaming throats. It's a lot easier to take steel off than to put it back on. The worst that can happen is some leading and that's easy to remove. You may find that it shoots fine. I've got a S&W with tight throats but it shoots great with cast bullets.

+1.

I'd also find a gunsmith or machinist with pins and pin measure the throats before I did anything like lapping or reaming.

Larry Gibson

[paul h]

If your throats really are 0.001" under bure size, accuracy with cast bullets will more than likely be horrible. IMHO throats should always be 0.0015-002" over bore diameter for top accuracy. I have one revolver with throats 0.003" over bore dia and it produces accuracy on par with what many would expect from a rifle.

[Petrol & Powder]

If your throats really are 0.001" under bure size, accuracy with cast bullets will more than likely be horrible. IMHO throats should always be 0.0015-002" over bore diameter for top accuracy. I have one revolver with throats 0.003" over bore dia and it produces accuracy on par with what many would expect from a rifle.

I agree that generally speaking the cylinder throats need to be a little larger diameter compared to the bore, but.... the proof is in the pudding OR the only poll that matters is the one on election day.
I have several revolvers of the same make and model. Some I had to open up the cylinder throats in order to make them shoot better and some I left as they were - because they shot just fine. There's NO harm in shooting it first and making a decision based on actual performance. It's highly likely that enlarging the throats so that they are slightly over the bore diameter will improve a revolver but if it shoots well as is - I would never alter it.

[Petrol & Powder]

As for price, I'm sure others on this forum can help you. I've rented reamers/pilots and I've been happy with that arrangement. The cost to purchase a reamer is high and that cost precludes a one time purchase for me. If you only have to use it for a day on a couple of guns, renting makes sense. If you think you will need one over some longer amount of time, buying one makes sense. Your call, but once you ream a cylinder you don't need the tool for that particular cylinder ever again.

[leftiye]

They's a bunch of (as in many many) threads here asking that question.

Don't be daunted, it ain't very hard. A dowel with sandpaper (320 or 220 grit) spun on a drill motor will do it. Enter from the rear and be careful that dowel stays centered in the chamber at the rear. This helps keep it straight. Don't spin too fast. Use a length of sandpaper that enters without a large amount of resistance. Clean and test for size with pin gauges often. Be careful to make them all friction fit the desired pin gauge the same.

Can also be done with a chucking reamer in a drill press, or a milling machine, or a lathe (zero on each chamber mouth in turn). This will work fine in most cases IF the reamer is not crooked. They are flexible and will center, but do not use a really crooked one as it will push to one side enough to make hole oversize. At least they do when modifying molds. Run slow, and use lots of oil for best finish.

[Tatume]

I have not tried the gun as-is. I've not fired it yet at all. Still, conventional wisdom says I've got the ingredients for trouble so I want the gun made dimensionally correct.

Shoot the gun. If it shoots well, keep it. If it doesn't shoot well, send it back to S&W and they will fix it.

If it ain't broke, don't fix it.

[Oreo]

Shoot the gun. If it shoots well, keep it. If it doesn't shoot well, send it back to S&W and they will fix it.

If it ain't broke, don't fix it.

Whatever the solution, I'm not going to wait months and months for S&W to get around to it. I'll buy a Bridgeport and take a class on machine work before I spend and wait for someone else to do it at their leisure. Principal of the matter.

[paul h]

I agree with shoot it first, but again my prediction is jacketed accuracy will be ok, but cast less than stellar. There is always an exception to the rule, but the throat will size the bullet smaller than the bore and a cast bullet smaller than the bore will have a tendency to dramatically open up groups.

While sandpaper around a dowel will work, it will tend to open up the front and rear of the throat more than the center creating an hourglass shape. The proper tools are not that much money, an adjustable lap and a couple tins of clover compound from MSC.

http://cdn.mscdirect.com/global/images/ProductImages/0506028-23.jpg

And a 0.431" decimal reamer will follow the original throat as well as a specialized gunsmith reamer, but at much lower cost.

http://cdn.mscdirect.com/global/images/ProductImages/7203431-23.jpg

[Tatume]

Well, if you want to buy a **** Bridgeport go ahead, but don't curse at me. My experience is S&W returns guns in a few days to a week or two.

[Oreo]

I'm sorry. I didn't mean to come across as quite that flippant. I appreciate the suggestion. I had heard bad things about S&W customer service. I think I'd rather send the cylinder to a reputable smith then the manufacturer if it needs that.

I have resolved to trying the gun before cutting, thanks to the majority consensus suggestion. I am expecting a lot of leading but I'll try and see.

[Silverboolit]

Did you slug the bore? If you did, take the slug and try to push it through the cylinder throats. If the slug passes easily, the throats are probably ok. I have done this several times and it works. Not as fancy as all the measuring, etc, . If the slug doesn't go through, the throats are smaller than the bore, and work is necessary.

[Oreo]

Did you slug the bore?...
So I have this new to me S&W 629-4 Mountain Gun. (44mag) I was just making impact slugs of the bore, forcing cone, and all six cylinder throats. Turns out all six cylinder throats are right at .4287", and the bore is .430"ish (5 grooves make precise measurement difficult)

So I guess that means I need to have the cylinder throats opened up to, what, .4310"? Can I buy a tool and do that myself or does it have to be done on heavy machine equipment by a smith?

Thanks for the help in advance.

Read the op next time. ;)

[detox]

I am doubting your measurements are accurate. You need to shoot the gun...i would use a soft alloy 20/1 at lower velocity at first then move up to harder alloy with faster velocities.

S&Ws almost always have “thread choke”, there the barrel is crushed a bit by the tight fit where screwed into the frame. This problem, and the use of “FIRE lapping” to try to correct it, is easily researched by a bit of Googling.

[Oreo]

I am familiar with thread choke and fire lapping.

Why do you doubt my measurements?

[bob208]

ok I will bite. just how did you get the measurements ?

[Oreo]

As I said in the first post, I made an impact slug. I used a dead-soft egg fishing sinker placed in each cylinder throat. Place cylinder face down on hard surface and with a brass rod and hammer whack the lead sinker so it conforms to the throat. It works very well. I could have made chamber casts with cerrosafe. I have some of that too, but I didn't want to deal with the expansion / contraction of the alloy screwing with the measurements. Anyway, once the impact slug has been fully beaten into submission, gently tap it out and I measure with a digital micrometer (not calipers for this.)

That sound ok to you guys for taking an accurate measurement?

[Mal Paso]

I am only familiar with the Manson reamer. Maybe the pilot bushing is overkill but I had good results. .431" is their standard size for 44 but their tolerance is 0 to +.0005". Manson will sell you the reamer with the bushing you need although I used both .428 and .4285 pilots on my Smith. S&W throats are cut for jackets now.

I believe you.

[leftiye]

As I said in the first post, I made an impact slug. I used a dead-soft egg fishing sinker placed in each cylinder throat. Place cylinder face down on hard surface and with a brass rod and hammer whack the lead sinker so it conforms to the throat. It works very well. I could have made chamber casts with cerrosafe. I have some of that too, but I didn't want to deal with the expansion / contraction of the alloy screwing with the measurements. Anyway, once the impact slug has been fully beaten into submission, gently tap it out and I measure with a digital micrometer (not calipers for this.)

That sound ok to you guys for taking an accurate measurement?

Yeah, is good. Easier (by no means critical), use pin gauges on chamber mouths. They are more accurate because you can use friction on sucessive holes (chamber mouths) to determine exactly equalness. They can be had cheaply, if you have a few xtra bucks sometime. (cheaply doesn't matter too much because you only have to grab your micrometer to check them). Five grooves, five lands of equal width (ten equal segments, divides by two). The leading edge of any given land on your slug is exactly opposite the trailing edge of the land opposite to it.

[Oreo]

The leading edge of any given land on your slug is exactly opposite the trailing edge of the land opposite to it.
This does not give you a through-the-center diameter. Check your geometry again.

[bob208]

there are several ways to measure a 3-5-7 or more sided part. flat mics is not one of them.
it is not just you. this is a rant that has been coming on this subject. I see guys throwing around dimensions and tolerances that would make a tool maker blush. on things they have no way to measure correctly.

then how are they going to make it right? well we are going to clamp it in a bench vise and hand wobble a reamer through the hole. or run that reamer in a drill press and push it through. first how do you know the reamer is even cutting to size? how do you know you are even getting it straight?

there is only one way to hand ream a cylinder. john taylor has posted pics of how to do it. the other is in a really good drill press with a lot of set up. a milling machine or a jig bore.

as I said this nothing personal. it is just a rant with questions.

[Tatume]

And all this is to "fix" a gun that hasn't been fired.

[Oreo]

And all this is to "fix" a gun that hasn't been fired.

That point has been made and acknowledged, thank-you.

[leftiye]

This does not give you a through-the-center diameter. Check your geometry again.

Not worth worrying about, even if you were right (which I don't think you are). You have five equal segments in each half. I was just trying to be helpful. Why ask for help and then argue about it? After all, you will do as you please anyway.

[Oreo]

I'm not trying to argue with you. I sincerely appreciate everyone who takes the time to reply.

[MtGun44]

Here is a relevant blast from the past.

http://castboolits.gunloads.com/showthread.php?12464-Revolver-throat-reaming-with-drill-press-mill

Bill

[kweidner]

I ream mine. I use pin guages and split dowel with sandpaper. World class sass shooter doubted the accuracy of my work until I let him measure them for himself. Go slow measure often. Don't do anything till you fired it. I have a ruger that is STUPID accurate from being reamed, firelapped, and a little trigger work. I can ring a 8x8 plate 6 out of six times at 100 with that little 4 5/8 bbl. It's almost comical and repeatable with boring regularity.One of my favorite past times is going to the range right before deer season to show the non believers that practice with a handgun and you can outshoot most weekend hunters rifle skills off a rest :). When I first started, Bill and the other guys helped me a ton. Thanks guys!

[MtGun44]

+1 on shooting it a good bit prior to doing ANYTHING.

Here is an important point to ALWAYS remember:

Each gun is a thing unto itself.

Just because it measures right or wrong, the darned thing
may not understand that it is either 'perfect' or 'messed up' and
the 'messed up' one may shoot well or the 'perfect one' may
shoot badly. Broadly speaking, fixing the dimensions has a
very high probability of improving things, but beware of the
statistical outliers.

Bill

[Good Cheer]

Over twenty years ago I cooked up a method of opening up cylinder throats using a drill, a spindle and a piece of emery cloth duct taped to it. At the time I was in correspondence with Veral about how to do it and that's what came of it. Make the direction of the cloth wrap open up against the bore of the throat due to rotation of the spindle. Go slow, check often and you can be pretty darn exacting of the results.
But if you're gonna take out a couple-few thou's then a precision reamer job would really be a better mouse trap. Have someone else double check your measurements because that's what Quality Assurance is all about. Worry about frame induced constriction if it doesn't shoot.

[Bret4207]

+1 on shooting it a good bit prior to doing ANYTHING.

Here is an important point to ALWAYS remember:

Each gun is a thing unto itself.

Just because it measures right or wrong, the darned thing
may not understand that it is either 'perfect' or 'messed up' and
the 'messed up' one may shoot well or the 'perfect one' may
shoot badly. Broadly speaking, fixing the dimensions has a
very high probability of improving things, but beware of the
statistical outliers.

Bill

X100! Don't touch anything till you've got a least a couple hundred rounds through it. God as my witness, grabbing a big hammer before something proves to be broken is not a good plan!

[pbcaster45]

My Model 10-10 wouldn't even pass 9mm jacketed bullets when I first got it. I sent the cylinder to David Clements and he opened them up to .3575. Here's a picture of the cylinder mouths after the work was completed. Leading went from pretty bad to nothing.

87883

[W.R.Buchanan]

I am going to pile on here, simply because I see a solution looking for a problem.

YOU NEED TO SHOOT THIS GUN BEFORE YOU DO ANYTHING TO IT !!!!!!!!!!!!!!!!! [smilie=w:

First your method of measuring the throats may be alright. However you have no idea exactly what the bore size is. :( You have no valid way to measure it.

Most S&W .44's I have seen had .429 barrels.

Just firing 50 Jacketed bullets thru that gun would burnish the throats to where they took out that .0003 you are worrying about. :!:

If the gun doesn't shoot well then send it back to S&W and have them fix it. They actually know what they are doing as opposed to others who may or may not know what they are doing.

Hearing that they have a a slow turn around time from some "*****" who is just spreading hate, is not a thing to base a sound decision on.

Since you don't sound like you have a mill or know how to run one, and don't know exactly how a reamer is going to cut even if you did, then chances are,,,and I am nearly 100% certain on this point,, that you would ruin the cylinder. This will be an expensive mistake and will require you to send the gun back to S&W anyway. [smilie=b:

I do have a mill along with 35 years of using it and reaming countless holes,,,, and I wouldn't do this job!

I would be learning on a critical part and the chances of failure are almost 100%. even at my level of expertise.

Shoot a couple hundred rounds and come back and tell us how the guns shoots.

Then we can discuss alternatives if necessary.

Trying to fix something that isn't broken is a very foolish route to take. [smilie=b:

You'll note that others have said the same thing several times in the above posts.

Time to listen to us now and hear us later. :mrgreen:

Randy

[Oreo]

I hear you.

I am certain that the bore is at least .4300" because that is the widest point in the cross section of the impact slugs from the bore. It might be bigger but it's definitely not smaller.

I asked the question in the original post because I am anticipating a problem. There is in fact a constriction. I will shoot the gun before modifying it but at least now I understand the solution ahead of time if there is in fact a problem. Maybe there won't be a problem. Time will tell and I'll keep my fingers crossed for that first range day with the gun.

The gun is not new. I bought it used so I doubt there will be any easy fast burnishing of the cylinder throats to remedy the constriction.

I respect your opinion on reaming the cylinder throats as informed by many years of professional experience. However, your opinion in this case is the exception. My research indicates this has been done by hand with good results by many people with far less experience.

ETA: I got my info on S&W's turn-around time by searching threads over on the S&W forum. I figure those guys ought to have reasonably accurate info on the subject.

[45sixgun]

I'm far from any expert, so take my experience with a grain of salt. I had a Ruger .45 with tight throats. I reamed them myself with the Manson reamer. I couldn't have been more inept at it either! Whew! You can read the thread about it here (http://castboolits.gunloads.com/showthread.php?146180-throats-in-my-45). I've also firelapped the gun. And this is how it shoots now. My new 44 special and (slightly used) .357 (both Ruger SA's) can't hold a candle to it for accuracy. I haven't done any work on them at all. I'm sure I just stumbled around where angels fear to tread, but it all ended up well for me.

https://lh5.googleusercontent.com/-Uy4ttsGFTeg/UVhDEfErN6I/AAAAAAAAatE/SppEcKs6F1Q/s800/P1120196-002.JPG

[paul h]

I'm kinda suprised someone claims to have vast machining experience would be afraid to tackle reaming/polishing a cylinder throat, it really isn't that difficult of a job. Machining a cylinder from scratch, that's a whole different ball game and not everyone is up to the task.

But there are plenty of methods to remove metal in a slow and controlled manor concentric with the existing throat that can be employed, and most revolvers will show a marked improvement in accuracy with cast bullets when the dimensions of the cylinder throat are in harmony with the dimensions of the barrels bore. For some strange reason many manufacturers produce cylinders that are too tight for top accuracy with cast bullets.

[MtGun44]

"For some strange reason many manufacturers produce cylinders that are too tight for top accuracy with cast bullets."

Manufacturers have near zero interest in cast, they are designing and testing with jacketed ammo. Their dimensions will
often work just fine with jacketed and frankly, they mostly couldn't give a rat's about whether they work with cast. - sad
to say.

Bill

[W.R.Buchanan]

Paulh: not saying I couldn't do it,,, I said I wouldn't do it.

Not when there are other better options. If S&W ruined this part then they would fix it. I would have to replace it and that wouldn't be easy.

Part of being a decent machinist is knowing your limits, and what you can do first time everytime, and what you might F up. Also understanding the odds of producing a perfect part on the first try.

When dealing with things in this category I generally defer to "them that knows" and people who do what they do every day. I also don't Blanchard grind parts or do super close tolerance work or other types of work that have shops that specialize in that unique type of work.

No shop can do it all. And the closest I have seen to "do it all" type individuals are gunsmiths. You will note that some are good, and some suck outright, just like in any other profession. Usually knowing his limits is the defining factor, between good and sucks.

I do mainly production style work where you have extra parts in case you screw one up. Learned that it is possible to screw up a part no matter how good you are, or think you are, more than 30 years ago.

This job is one shot to make it right and if you fail or have any glitch you lose big. Odds are against a perfect result in this particular situation using the tools described above.

Another fine point missed here is that the chambering reamer for these guns does the throat and the chamber all in one swipe so it is impossible for them to mess it up unless the reamer is worn or bad or drags a chip or runs out of coolant. Trying to take out .001 with a regular chucking reamer in Cromoly could easily take out .002 or more and you wouldn't even know it. If the reamer is cocked at all or doesn't hit the hole right it will take out more.

You can't put it back.

I don't ream holes in expensive parts made of Cromoly frequently. This material is problematic at best. All it takes to ruin this part is to have the reamer go in a little cockeyed or drag a chip or many other things, on any one of the six holes.

I would only do this job if,,, There was no other way to do it and no one else would do it, and most importantly If I really HAD to do it, and had the correct "Piloted Reamer to do the job. I would still sweat blood over the job.

In all cases it is not worth it to attempt this kind of work when there is a factory that will do it for free or very little $, and all you have to do is send it to them. The cost of the reamer alone is more than the postage.

Incidentally, I actually own a machine shop and am siting in there right now writing this .

Randy

[fourarmed]

I have used the split shaft and emery cloth, and it worked well enough, but the last time I did it, I got a little fancier. I used pin gauges to determine the throat diameter, and I also found the largest gauge that would fully enter the chamber and stop at the throat restriction. Using aluminum rod, I lathe-turned a piece to the larger diameter, then turned the end of it down to a diameter 0.040" smaller than my target throat diameter. (My emery cloth is about 0.021" thick.) The smaller part was just slightly longer than the throats. I slit that part, and put the emery cloth around it. I then ran the unit in from the chamber end and turned it by hand. It didn't take much to gain a thousandth. Probably took three strips of emery to open all six throats that much. I like this method because the larger diameter keeps the cutting part centered in the throat.

Oh yeah, opening my M57 Smith from .410 to .411 shrank groups with cast bullets about in half.

[45sixgun]

You can't put it back. So true.

When I reamed my cylinders for the .45, I really messed things up. I'm mechanically inept to the extreme and screwed up what should have been a simple job. I took a nice divot out of the side of the cylinder by not keeping the reamer straight. Yeah, I know....really pathetic. But I posted the type of groups it's shooting. I've tested that one cylinder over and over. It's no less accurate than the others, and it doesn't seem to be adversely affecting the brass.

https://lh5.googleusercontent.com/-AJTkS93e-ZE/T0RNLOQ0y7I/AAAAAAAAaKc/RSiG6F7ulnw/s800/P1050161-1.JPG

[paul h]

That should be within the web of the case. You'd have to load a 44 really, really hot to get it to expand into the web.

[leftiye]

I have used the split shaft and emery cloth, and it worked well enough, but the last time I did it, I got a little fancier. I used pin gauges to determine the throat diameter, and I also found the largest gauge that would fully enter the chamber and stop at the throat restriction. Using aluminum rod, I lathe-turned a piece to the larger diameter, then turned the end of it down to a diameter 0.040" smaller than my target throat diameter. (My emery cloth is about 0.021" thick.) The smaller part was just slightly longer than the throats. I slit that part, and put the emery cloth around it. I then ran the unit in from the chamber end and turned it by hand. It didn't take much to gain a thousandth. Probably took three strips of emery to open all six throats that much. I like this method because the larger diameter keeps the cutting part centered in the throat. P.S. where the sanding does round the entry edge, if entry is from the rear, all this does is taper and smooth the transition from case diameter to throat.

Oh yeah, opening my M57 Smith from .410 to .411 shrank groups with cast bullets about in half.

Not trying to be a pizzant here, but. The split dowell/shaft etc. will self center really well by itself. Where your stepped cylinder fitting shaft would be great is in keeping the whole thang straight whilst abrading the chamber mouths. Use oil in chambers! P.S. while using sandpaper on a shaft does round the entry corners, all this does when entry is from the rear of chamber is to taper and smooth the transition from chamber to chamber mouth.

[W.R.Buchanan]

It wouldn't be wrong to chamfer the mouths of the chambers for easier loading as well. And this is something I would do. But the pitfalls I have described above and shown by ".45Sixgun" are the type of thing that happens when you don't know exactly what is going to happen.

The only ways around this are to either have a fool proof tool to do the job, or enough experience doing the job so as to know what is going to happen when the reamer bites.

If I had a cylinder fixture made up or indicated every hole before I stuck a reamer into it, I would have a pretty good chance of having the reamer go in the hole strait,,, On my milling machine. On a drill press this is a disaster waiting to happen.

I have two 44 revolvers. A Super BH Bisley and a BH Bisley. The chambers on the BH Bisley are perfect with no significant tool marks showing that the reamer was in good shape and mucho coolant was present all the way thru the process.

The Super BH Bisley's chambers look like 30 miles of bad road, however they don't affect the accuracy of the gun in the slightest. The tool marks left behind were caused by either a worn reamer dragging a chip thru the cut, loss of coolant during the cut,,,, Or here's one you haven't considered,,, The grain structure of this particular piece of Cro-Moly steel!

Cro-moly steels vary greatly in composition from supplier to supplier. If the cut was across the grain like if the grain is running lengthwise in the bar then it will smear easier than if the grain was running across the bar.

The only way to combat this, since you will never know which way the grain is actually running until after you make the cut, is to have very sharp tools and/or tools made from exotic materials.

It is not uncommon for shops to use Diamond alloy cutting tools when machining Cro-moly for Aerospace uses, and typically the material is pre-hardened so that when the machining takes place it isn't contingent on anticipating how heat treating after the fact is going to change the final dimensions, and the part can be machined to final dimensions which will not change.

This is also done at very high speeds, and the finishes generated by this process are second to none.

I assure you that Ruger is not doing it this way. They are using CNC milling centers and more conventional tools simply because the tolerance range of their parts is well in excess of anything made for Boeing and is not required for a handgun in any event.

I am on my way now to farm some work out to another shop simply because It needs to get done faster than I know I will be able to get it done.

IE: I know my limits.

Randy