Space between cylinder and barrel (637)


December 13, 2008, 09:40 AM
Yesterday I shot a new 637 S&W 38+P with some reloads. The build up carbon ring at the end of the cylinder was just tall enough to rub the cylinder and I could not pull the double action as the drag was to great. It took a few minutes to find the problem. I think the barrel is too close to the cylinder. It looks to be about .010" or so. If I clean the carbon ring it will shoot 10 more before it touches again. Maybe I'll have to send it in for an adustment??? Does anybody know a correct distance between the two?

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Pistol Toter
December 13, 2008, 09:46 AM
.004 -.006 is ideal, my carry Ruger Sp101 is @ .002. The .010 to me is pretty large even though I have seen .012, that's a lot. I would suggest you try a different brand of ammo. Sounds like what you are using is dirty. My 2 cents.

December 13, 2008, 09:59 AM
You are right about the dirty loads. I tried some AA#5 as a suggestion and it needs a lot of cleaning when done. I'm a little disturbed to here the .006" because my newer 642 has about .009 on the top and about .018 on the bottom. When I bought the 642 new I noticed it but it runs well. Also i'm a newbie with revolvers with 10 years of automatics under my belt. I'll try to get a pic of both peices and post them.

The Bushmaster
December 13, 2008, 10:13 AM
Go to a cleaner burning powder like W-231 and your problem will go away. .010, to some manufacturers, is excessive cylinder to barrel gap.

Pistol Toter
December 13, 2008, 10:13 AM
There is something wrong with that 642; it should be the same between the top and the bottom. Do you have an accuracy problem with that gun or does it not spew lead and powder. .018 is enough to pass an aircraft carrier through and not scrape the sides of the ship. LOL I've got 30+ year old S&W that don't go over .005 - .007 and most are on the lower end and down to .004. I don't have any trouble with the Ruger @ .002 but I use Remington or Speer or Federal mmunitions.

PS: Sounds like you've got a misaligned yoke or the barrel that needs to be removed the cone . breech dressed, the barrel re-cut and threaded and properly reinstalled.

December 13, 2008, 10:26 AM
It looks to be about .010"

"looks" to be? It's dang hard to judge these by eye without a lot of experience at it. Read the sticky above in this forum by Jim March about the proper way to judge this. The feeler gauge set you will need is not common - it will require .001" increments from .002" to .014" or more.

If this is a modern gun, don't fret, you can send it back to S&W for warranty repair. I agree with Pistol Toter that if you have measured the 642 correctly, that is not acceptable. Read the check out, measure it again, and if it's like that, then call S&W and they should send you a call tag to send it back to them w/o expense on your part.

Pistol Toter
December 13, 2008, 10:47 AM
Oro is correct in not being very common, but they can be found without a lot of effort. I have a set Of Mitutoyo that start at .001, .0015, .002 and right on up. The hole set must be close to .50" thick. Between them my Fowler vernier calipers and several Starett micrometers and Starett machinist scales, I can measure most anything. If you don't have the equipment let somebody else look at and measure the b/c gap also check the end shake, the barrel to cylinder alignment with a range rod and the yoke alignment. Revolvers are tough but hard or miss handleing / use can be detrimental to an otherwise fine gun. Sometimes S&W turns loose guns that ought not have left the factory and NOTHING is made like it used to be. There is little craftsmanship of pride left in the work place.

December 13, 2008, 10:54 AM
the other end. My Redhawk was binding and I couldn't shoot it DA. Crud had accumulated under the ejection star and the rears of the cases were rubbing. Cleaning cured it.
Good luck.

December 13, 2008, 01:56 PM
In the armorer class they teach to come in from the left side, at the top of the frame window, using Go/No-Go gauges to measure the cylinder gap. The acceptable range taught in the armorer class is .004" - .010".

Conditions which might cause inconsistent or rough cylinder rotation could be an improper yoke line up, a loose/bent extractor rod or simply dirt/debris under the extractor.

Just some thoughts for the sake of polite discussion, though. Don't have any way of knowing what's happening with your gun. Best to call and discuss it with S&W.

S&W has excellent customer service if you believe your 637 requires service. Call them and discuss your concerns with them and see what they say. Ask to speak to a repair technician (if possible). They'll pay for shipping both ways for warranty repair.

BTW, they go on their usual 2-week holiday break starting Dec 22nd.

Old Fuff
December 13, 2008, 02:57 PM
Sometimes the problem is caused by leading, not carbon build-up. Back during the days when most revolver ammunition (factory and reloaded) used soft, swaged lead bullets cylinder/barrel gaps tended to be wider - in the .006" to .012" area. When the switch to high-performance loads using jacketed hollow-point bullets came along manifacturers' were pressured by customers to tighten the gap down to around .003" - .006" - which wasn't always a good idea.

The gap should always be measured with feeler guages, and never eyeballed.

December 13, 2008, 03:02 PM
A lot of very good info. I did get a go no go gauge but it is just small enought to fit.(Crafstman) The 637 is a tight .006 and it will not slip into the .008. But Now my big problem is the 642. It measures .008 on top and the bottom is by far larger. I could not measure the bottom because the gauge is too wide but i'm guessing .012 to .015. Here is a picture of it. On my way back today I stopped at another gun shop and looked at another 642 and it looks exactly the same. The 642 shoots very well and holds very nice groups at close range. I think I will take your advice and call S&W.

December 13, 2008, 03:19 PM
It looks to me like the forcing cone was not cut square. Definitely send it back to S&W, they'll make it right.

December 13, 2008, 03:49 PM
^ agreed.

December 13, 2008, 04:07 PM
Don't let your eyes fool you into doing something silly to the rear of the barrel. An improperly aligned yoke can fool you. Also, yokes are 'paired' with frames during production. You don't want to fool with one and damage it. Call S&W.

December 13, 2008, 08:19 PM
Obviously I will send it back. But can I ask. What will this forcing cone miscut face do? Is it dangerous? What will happen if the space is .015" or .020"? Just want to know for good information. ALSO... What would happen over time if I never noticed it? Kind of disturbing!

December 13, 2008, 10:00 PM
Holy cow! I just had the bottom measured and it is .026" gap. I just had a lesson from a very experienced gun smith. He said that may be the reason I had a squib load a while back when I switch to a shorter 125 grain bullet. He advised the shorter bullet crossed from the cylinder to the cone and that gap is opened more quickly and the powder did not stay under pressure long enough to fully burn. That explained all the unburnt powder when I had a squib. I feel more relieved to find out all this info today. It was driving me crazy. Thanks to you guys for keeping me on it -vs- my original thoughts of just ignoring it. Safety first.

Old Fuff
December 13, 2008, 10:48 PM
Swing out the cylinder and look at the frame under the barrel. there could be a crack in the thin area. Also check the barrel forcing cone at 6:00.

Another possibility is that the barrel hole drilled in the frame isn't straight, which would cause the barrel to be angled, top to bottom.

December 13, 2008, 11:19 PM
When the gun becomes dirty from shooting the cylinder will turn less and less smootly on the transfer bar. The "stuck" cylinder will then lift and tilt, lean onto the end of the barrel, upon the hand poking the cylinder for a turn to the next chamber.

If the barrel gap varies as the cylinder turns when the gun is clean you can sand the front of the cylinder, but only where needed.

If the barrel gap is indeed too small on all chambers you can sand the end of the barrel.

Old Fuff
December 13, 2008, 11:54 PM
If the barrel gap is indeed too small on all chambers you can sand the end of the barrel.

I sure hope not! :eek:

If the cylinder has developed end shake (back & forth movement) it will wear in a forward direction until the face of the cylinder hits the back of the barrel. If you remove metal from the back of the barrel the cylinder can continue to move forward. At the rear you are increasing headspace, and eventually the cartridges will fail to fire because of light hits.

The correct solution is to move the cylinder backwards, away from the barrel. Then the barrel and cylinder will cease to rub.

It wll come as a shock to some, but I understand that the factory is well equipped and has experienced workmen who can quickly take care of the problem. Why not use their services?

Ron James
December 14, 2008, 12:04 AM
Gosh Old Fluff ! Are you saying that the people who made the gun know how to repair it?:)

Old Fuff
December 14, 2008, 12:43 AM
Gosh Old Fluff ! Are you saying that the people who made the gun know how to repair it

Well it was a thought... :uhoh:

The Old Fuff is a skinflint of the highest order... "Cheap" is too mild a word. :D

Now if the job is done correctly some specialized tooling is required, and buying a +/- $30.00 shop manual can save you a lot of trouble. But all of this adds up to some serious $$$.

In addition a little bird told me that this problem might require a barrel or frame replacement. Hardly anything I'd want just anybody too do on his basement workbench.

If I play my cards right I can get the folks at Smith & Wesson to go over the entire gun and fix anything and everything they find is wrong.

And they will do the entire job for free, and even pay the back & forth shipping costs.

So that means I can save all of my own bucks for more important things, like ammunition, accessories - and even more guns.

So I don't see it as a hard choice to make... :cool:

December 14, 2008, 03:46 AM
Yep, best to let the factory examine & repair (or replace) it at their expense. ;)

December 14, 2008, 06:13 AM
LOL! The factory? I don't see a need of that. If you've got a large crescent wrench you should be able to tweak the frame back to square, and a big pair of waterpump pliers to squeeze the two legs of the yoke together and you'll be good to go. does look to me like the barrel/frame is straight enough but the cylinder is badly out of whack for whatever reason. Please send it to the factory and do not shoot it no mo'.

I'm surprised that we don't see more like this considering the types of ammo that some people claim to be shooting from the little aluminum darlings.

December 14, 2008, 09:35 AM
I'm a pretty decent metal worker in some ways. I can tell the back of the barrel was cut at an angle. It may have bin ground by a machine or cut with a saw but it was not milled.

The same Smith measured my 637 and at 6 oclock the gap is .011 and at 12 oclock it is .006". Every J frame I have is similar to this and every J frame I looked at new in the guns shops are like this.

Are S&W assemblers using a belt sander to set this gap???

Old Fuff
December 14, 2008, 10:08 AM
A lot can depend on when the revolver was made. Back when barrels were one piece, the shoulder would be adjusted so that when it was screwed tight the front sight would be at 12:00. If that left the cylinder/barrel gap too tight it was "corrected" with a file. How well this was done depended on the skill of the person doing it, and how much time he was allowed to do it. If the barrel isn't square the only way to fix it is to remove the barrel, put it in a fixture and turn it so it is square, and then take enough off of the shoulder so that it can be rotated another turn to take up the excessive gap. Notice that the gap between the underlug on the barrel and the end of the ejector rod is considerable. That isn't good but it does allow for adjusting the barrel as described above.

These days the barrel is a tube that is threded in to a crush fit. Then a sleeve with the front sight and underlug is slipped over it. The sleeve is held with a nut at the muzzle end, and when everything is set the muzzle is faced off. In theory it should not be necessary to do any filing at the back end, but I'm not sure if they do so or not.

The only good thing I can say is that they will fix it, and they'll do it on their dime.

Random Discharge
December 14, 2008, 10:11 AM
Anyone ever think about just how easy it is for a gun owner to check b/c gap?

Isn't it amazing that Smith, Ruger, Taurus, you name them; with all their specialized factory tooling; can't get this right? Maybe they don't have feeler guages at the factory, so they can't inspect this before shipping the new guns?

Or maybe, once built wrong, it is expensive (new barrel) or time consuming (threading barrel in another turn-also expensive due to labor) to fix? Why inspect the b/c gap when you can ship out a slew of improperly built guns and only have to repair or rework the few that come back? Even better, increase the "official" maximum specification enough so that most of the improperly built guns can't even come back as warranty repairs...

Sadly, it shouldn't be difficult to get this dimension right the first time.

The only message the manufacturers will understand is the cost of warranty repairs. If it ain't right, by all means send it back!

December 14, 2008, 10:42 AM
Random Discharge , Exactly...

"Why inspect the b/c gap when you can ship out a slew of improperly built guns and only have to repair or rework the few that come back".

I removed your "?"

I just want to back up Old FUFF.. About a year ago he helped me repair a black powder gun...

If you get down on your knees and beg, once he understands you have tools, and maybe a few working brain cells he will help you.

The thing is you need to do what he tells you to do, the way he tells you to do it.

And that cylinder to forcing cone is pooched.. Send it back.

Old Fuff
December 14, 2008, 11:19 AM
Well thanks for the plug. :)

But there are problems. :(

You can't always diagnose the cause of a mis-functioning gun over the internet, and often times fixing something, and doing it right - not just doing it, requires experience, knowledge, and maybe some specialized tools. A shop manual (if available) is also a must if you are going to do your own work.

If one is looking at fixing "a" gun, the cost of getting everything together may be more then getting a professional to do the job, and this is especially true if the cause of whatever's wrong isn't certain. If for example, the barrel has to be removed and fixed or replaced, or the issue turns out to be an out-of-spec frame, you will be way passed a do-it-yourself job.

Shouldn't they have caught this at the factory? You bet they should! Especially on a model that is commonly sold as a personal defense weapon. But now days that simply doesn't happen, and frankly if they did it right on a 100% basis you might not be able to afford the gun. So the buyer is stuck between a rock and a hard place.

The good thing here is that if it's returned to S&W they will completely check it out, and fix anything they find wrong, and they will do it on their dime - including shipping costs.

December 14, 2008, 11:28 AM
I'm currently on my 3rd and 4th handgun. I learn more and more about how a handgun works by cleaning and disassembling them. Being technically inclined and no stranger to analyzing problems in general helps too. There are indeed many faulty guns floating about out there, especially on the Internet where owners want to dump their unwanded ones. A gun store that allows you to handle their guns is the best way to ensure a functioning gun. On the Internet a serious seller must have a good track record and be more than willing to accept a return. I handled a S&W 64, 38 spl 4" barrel this summer in Cabela's in Gonzales, LA. Tight barrel gap, timing stop on. It looked excellent, unfired, new old stock, $399. After a while I noticed that the barrel was slightly, slightly off, pointing to the left. It turned into a cold fish in my hands.

December 14, 2008, 05:13 PM
Yep, something to consider is that old and new production methods are quite a bit different.

I also like to hear the thoughts and reflections of Old Fuff. ;)

Some trivia from an armorer class a while back ...

It took 7 machines to make the old style S&W revolver hammers. It's considerably simpler nowadays with MIM hammers.

The older frames required 75 machining steps (without counting the barrel), and the newer frames only require 3 machining steps before heat treating. CNC has changed things.

I remember being told that S&W invested something like $17 million in new CNC equipment for the last fiscal year, and almost that much in the preceding couple of years, and that some shifts were being revised to allow round-the-clock operation of CNC machines (except for routine maintenance).

Personally, I was singularly unimpressed with the quality control of S&W revolvers in the 70's, 80's & 90's.

I'm reserving judgment on the ones being turned out in the 21st century. I want to see more.

However, I've received some with decent quality examples in the last several years.

Three of the last four J-frames I've bought have all exhibited reasonably good quality and fitting during assembly. This is compared to one I bought in the 90's which immediately required repair NIB before it would cycle and the trigger would reset.

I wasn't completely pleased with the fitting of the extractor and carry up on fourth J-frame, but it was relatively easy to correct. The factory would've done it for free if I'd returned it to them. It also had a rather noticeable deep, beveled scratch in the black finish around the yoke screw which had apparently been 'touched up' with a marking pen of some sort, and which revealed itself as soon as I cleaned the gun the first time. :scrutiny: In my case I shrugged and moved on, since that J-frame was really only intended for rotation in my off-duty carry but heavier and more frequent range sessions than my other J-frames, and I expected it would soon acquire the normal wear and tear associated with that role. Annoying, though. Sloppy on the production line.

Personally, I don't think the company is turning out a "slew of improperly built guns". Granted, I'd like to see some additional time and effort lavished on them before they left the factory, but that would reasonably cost more money. Where do you think we should draw the line? How much more money are we willing to pay for more 'hand-fitting' when assembling MIM components, or going back to forged/machined parts in some of the models? I remember when one fellow at the factory casually commented that they were trying to keep costs within reason so they didn't have to have parts production out-sourced to some country where labor was cheaper.

BTW, even investing in the 'basic' armorer tools for repairing simple problems with S&W revolvers can require some outlay of cash. The standard revolver armorer kit from S&W costs over $300, and it doesn't include some tools many folks might consider desirable.

The company is facing the task of balancing 'practical' against 'fashionable', and 'function' against 'appearance' in some respects. I don't envy them the decisions facing them in this slowing economy.

December 15, 2008, 08:16 AM
FastBolt, I'm going to ask S&W today if they will take this gun back and fix it. My question is how dangerous is this gap problem? (i'm new to revolvers). If they strive for .004 to .006 and mine is .026 it sounds dangerous. I do not have an agenda for this question other than good old knowledge. Every thread I have read said "Don't shoot it again?" Also this is a 6 month old 642 with about 400 rounds through it. They were all FN Plated or jacketed bullets no lead yet.

Thanks again for all of this info guys, if it gets annoying let me know. I feel like a kid asking why, why , why... :-)

Old Fuff
December 15, 2008, 08:44 AM
The danger, such as it is, is that when using lead bullets you might get excessive side-spit at the gap, with flame, flash and lead particles. This wouldn’t be so bad for you, but it could make things miserable for anyone standing next to you.

But there are two issues that Smith & Wesson needs to resolve. First, the gap may be an indicator of a more serious problem that might require replacing the frame, barrel, yoke, cylinder– or any combination thereof. Second, it isn’t right! So it should be made right. Considering the cost there is no excuse for this kind of workmanship and lack of proper inspection.

December 15, 2008, 08:58 AM
Old fluff, my friend is a NRA CCW instructor and he told me that lately within the past couple of years has had to ask other people to step back from the line while a revolver shooter is qualifying as the are getting sprayed. He always wondered why the tolerances were getting so loose. Small World!

I'll let you guy's know what S&W says today. It sounds like they will fix it with no questions. They always have been good to me on the automatics.

December 15, 2008, 09:21 AM
What will this forcing cone miscut face do?
Here's what it did in my Model 29-2:

1. Shaves lead and jacket material causing "spitting". This is dangerous and can cause facial and especially eye injury.

2. Directs powder gasses at the shooter and those to the sides.

I bought my gun used. As far as I know, the gun came that way from the factory. The fix is to machine the rear face of the forcing cone square, then turn back the barrel hood if necessary to allow the barrel to be screwed in enough to have the proper barrel/cylinder gap.

December 15, 2008, 09:26 AM
The danger, such as it is, is that when using lead bullets you might get excessive side-spit at the gap, with flame, flash and lead particles. This wouldn’t be so bad for you, but it could make things miserable for anyone standing next to you.
It'll do it with jacket material as well, as my 29-2 did.

In addition to the forcing cone being assymetrical, mine was dished up the center, directing high velocity powder gases straight up toward the top strap, like a half chimney. This caused the powder gasses, lead and jacket material to be directed not just to the sides but backward at the shooter, especially on the left side.

The forcing cone had to be machined square, and the barrel hood turned back for proper indexing... then they damaged the barrel and the whole thing had to be done again, including a total reblue. :rolleyes:

December 16, 2008, 10:08 AM
I am so absolutely confused my eye's are crossed. I emailed S&W with the information of the over sized b/c gap and they say it is okay. Here is a cut and paste from my email.:confused::confused::confused:

RE: 642 repair question‏
From: Ogonowski, Mel (
Sent: Tue 12/16/08 8:30 AM
To: 'Gary' (
yes the gap is fine

-----Original Message-----
From: []On Behalf Of Gary ******
Sent: Saturday, December 13, 2008 8:50 PM
To: Smith & Wesson Support
Subject: 642 repair question

To whom it may concern, I bought a new 642 revolver from a local shop and found the gap between the cylinder face and the barrel cone is .008" on the top and .021" on the bottom. The barrel is cut at an angle. It shoots well. And no problems are accuring that I know of. But everybody I talked to said that gap should be no more than .006" total and it should be absolutly straight. Does it need fixed? Also I just stopped at a local gun retailer and looked at a new 642 and it looks exactly the same with a angled cut. I attached a picture in .jpg. Can you tell me if it is okay or not.

Thank you,

December 16, 2008, 10:31 AM
Different gun than the start of the thread. I'm going to start a new thread. Oops.

Old Fuff
December 16, 2008, 10:50 AM
4$bill: :D

I would telephone Smith & Wesson and ask to talk to a gunsmith in the repair department, not someone in customer service. I'm not sure that Mel is qualified to answer your question. There is no company in the industry that where a .021" gap is within specification. Insist that you want your revolver inspected and repaired, and keep going up the ladder until you find someone with the authority to say, O.K.

They really do not want this spread all over the Internet... :evil:

(800) 331-0852 or (413) 781-8300

December 16, 2008, 12:24 PM
Call and ask to be connected to a technician in Revolver Repair concerning a warranty repair. Be prepared to leave your name, a brief message & phone number on the revolver repair center's voice mail if one of the fellows doesn't answer the phone when your call is transferred.

Okay, I just saw you started the new thread ...

Let them examine the gun and correct the problem. Enough said.

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