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S&W Revolvers: 1980 to the Present All NON-PINNED Barrels, the L-Frames, and the New Era Revolvers


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Old 06-29-2009, 07:44 AM
scooter123 scooter123 is offline
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Default Question about rifling

Did a good cleaning on the barrel of my 620 this weekend and just noticed that the rifling on the barrel was a bit different than my other gons, it's not hard edged but is "blended". Basically, if I take a sharp pencil and slide it from a groove to the land it will just slide without catching on an edge and on close examination with magnification it's obvious that it's radiused at both the land edge and bottom of the grooves. Round count is low, under 500 at this point, and I have found that the gun is EXTREMELY accurate off the bench. I've also noticed that the surface of the barrel is much shinier than it is on most of my other pistols, almost looks like it's been lapped.

BTW, normal cleaning practice is to patch the barrel with Kleen Bore Lead Away patches and follow up with solvent soaked patches and the dry, I try to avoid using brass brushes on my barrels.

Question, what is this type of rifling called and is it a type of rifling where shooting cast bullet would be a bad idea as it is in what Glock uses? Also, is it specific to the 2 part barrels or is S&W using this on the one piece barrels also?
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Old 06-29-2009, 08:07 AM
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I"ve heard it called both EDM, and CDM. I don't know which it is for sure. Brian Pearce of Handloader calls it EDM, but my buddy talked to a gunsmith friend of his who worked for Smith, and he calls it CDM.

It will work fine with lead. Although it doesn't usually shoot as well as cut rifling for that purpose, it will generally shoot lead better than most of us can hold on target.

My 586-4 that was built in '95, has that type of rifling, and from what I can find out, that is just about when Smith went to that type of system. It is faster for them to produce, with better consistancy, those being the two main reasons for the switch.

I hope that helps.
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Old 06-29-2009, 12:50 PM
Kevin G Kevin G is offline
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Default I"ve heard it called both EDM, and CDM.

Gun 4 Fun, Any idea if this is some type of chemical proccess?
My reason for asking is that a few months ago I had a tour of the S&W Plant and I thought I heard the tour guide make mention of some type of chemical proccess used to cut rifling. Never got the chance to ask about it before the conversation shifted and so did my mind. Have thought several times about asking here but have been reluctant until now. Stupid question type thing, and yes I know the only stupid question is the one that goes unasked. Tks, Kevin
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Old 06-29-2009, 05:39 PM
Gun 4 Fun Gun 4 Fun is offline
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Gun 4 Fun, Any idea if this is some type of chemical proccess?
My reason for asking is that a few months ago I had a tour of the S&W Plant and I thought I heard the tour guide make mention of some type of chemical proccess used to cut rifling. Never got the chance to ask about it before the conversation shifted and so did my mind. Have thought several times about asking here but have been reluctant until now. Stupid question type thing, and yes I know the only stupid question is the one that goes unasked. Tks, Kevin
From what my friend told me, (his handle here is Flat Top) his buddy that worked at S&W said it was indeed some sort of a chemical process that forms the rifling. whatever it is, they shoot great with that rifling style, and I'm including lead because I shoot a lot of it. I own two Smiths with this type of rifling.
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Old 06-29-2009, 06:26 PM
scooter123 scooter123 is offline
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Now that some clues have been provided, I suspect that the method used is Carbon Electrode Discharge Machining. It's an EDM process that uses a carbon electrode that is "sunk" into the workpiece. If that is the process they are using, S&W has learned a few tricks that I am unaware of, while it's a very precise process it's also been pretty slow in my limited experience with it.
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Old 06-29-2009, 06:54 PM
Dale53 Dale53 is offline
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C.E. Harris (on the Cast Bullet ***'n Forum) was quite critical of the EDM process for rifling a barrel. I have no opinion. However, if my 625-6 or 625-8 are EDM'ed then there is NOTHING wrong with it for accuracy. I shoot NOTHING but cast bullets and they are some of the most accurate revolvers I own. The rifling in the 625's is narrow and apparently six grooved (not at all like the "normal" five groove Smith and Wesson type). Whatever it is, it sure works with target loads.

Dale53
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Old 06-29-2009, 07:08 PM
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Default They were experimenting with EDM......

Back in 1995, while attending the annual S&WCA show in Springfield, we had the opportunity to visit the factory. They showed our group the EDM barrel rifling machine they were experimenting with and also shared some interesting rumor/info.
Apparently the process was so precise, and repeatable from barrel to barrel (read: exactly the same), that the BATF visited them and promptly registered some sort of request/reservation that the process would make it very hard to get unique "barrel signatures" on bullets, potentially causing some interesting challenges for law enforcement. The person giving us the tour suggested that they were thinking about ways to introduce "flaws" in the process so as to keep this from being a problem.
This is, from my recollection, what was indicated to us. The machine was new to them and I'm not sure it had gone into full scale production as of yet.
Just an interesting piece of info, maybe bogus, but the newer technologies (i.e., CNC) were being implemented by the factory to streamline and enhance production techniques pretty agressively back them.
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Old 06-29-2009, 09:18 PM
jrm53 jrm53 is offline
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Default Edm

If it is EDM I think they would have to have an electrode made from very dense graphite in the shape of bullet form with the lands and grooves in it, a male form of bullet and the barrel bore would be almost the small I.D. the EDM machine would be CNC controled with the twist rate figured at so many degrees per inch. I dont know that this is how S&W does it but the place where I worked for 41 years used this type of eguipment in punch and mold makeing. In 1988 they bought a company in Alabama that make the button rifleing buttons for Colt for the AR15's and M16's I had the tool room guys make me a .357 button with 1-10 twist to try to make my own barrels, they tic-tin coated it for me I reamed a barrel blank to the small dia. and tried to press the button through. Its still in the barrel, but Colt supposedly just pressed the rifleing reamer through the barrel bore. EDM would work with great equipment and skilled operators.
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Old 06-30-2009, 11:49 PM
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The process S&W has used for several years now for rifling center-fire barrels is EDM, Electrical Discharge Machining. This is the same process used by Magna-port to cut recoil reduction ports in barrels as it leaves a smooth finish and no burrs. It is done submerged in a liquid bath and leaves the bore exceptionally smooth but with slightly rounded corners instead of sharp square ones as the immediately preceding broaching system. They have been using the process for many years to made forging dies for some fairly complicated parts used in their guns. What I am certain of is the safety/decocker levers for the automatics. EDM was used to machine the recess in the forging dies for these parts that allowed the part to be forged including the grooving in the surface of the lever.

Unless they have discovered something fairly recently the .22 barrels are still broach cut as the bore is too small for EDM.

One advantage of the EDM rifling process is barrels do not have the so-called frame choke which is common with broach-cutting.

S&W did have dimensional control problems with early EDM barrels. Whether it was duration or voltage variations were the culprit some barrels came out with some odd dimensions. Some were a little tight and some were quite oversize.

I had an early EDM rifled .44 Mountain Gun which had normal cylinder throats (ball-seat actually) but the groove diameter was .435. And, yes, I have the proper tooling to accurately measure a 5 groove barrel slug if you wish to argue this point. The thing wouldn't shoot in a bucket with cast bullets. After lapping a mould so it would throw bullets at .436, a custom lubri-sizer die for .435 (sized .4355), and reamed the throats to .437 it actually shot very well. What a pain! To accomplish this also required reaming the brass as deep as the bullet shank seated using a .435 reamer in as-fired cases which removed about .0015" from the case wall. That was necessary so the ammunition loaded with the .435+ bullets could be chambered. Then I sold it. Now the cases that were reamed are un-usable as they are so thin that none of my sizers will reduce it enough to hold a .431 or smaller bullet.

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Old 07-30-2016, 07:11 PM
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Default Mountain Gun EDM rifling

To Alk8944:

Very interesting information on your discussion of EDM rifling on your Mountain Gun. Do you remember, what was the year of manufacture for the Mountain Gun you mentioned (with the 435 diameter)? Based on the dimensions you referenced, I assume this was a 44 Mag cartridge in either a 29 or 629 Mtn. Gun?

Did S&W change to EDM in 95?
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Old 07-30-2016, 07:56 PM
Pisgah Pisgah is offline
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Firearms History, Technology & Development: Rifling: Manufacturing: Electro Chemical Machining
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Old 07-31-2016, 09:50 AM
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The EDM (Electrical Discharge Machine) isn't new technology. GM Tool and Die shops used it in the mid to late 60's to burn out broken taps and cut hole that were otherwise hard to machine. Back then, it was a slow process, especially when removing taps, because you were burning away a lot of material. S&W is undoubtedly only doing the rifling, after having drilled a hole near or at bore size, which would speed the process immensely. The addition of chemicals to the process may speed it was well, as when we used it back in the 60's oil was used, not as an aid in the process so much, rather to clean away burnt material.

The process is extremely close tolerance, and should leave a far smoother bore than broaching does. In any cutting process like broaching, you are literally ripping the metal off the surface, no matter how little material you take with each cutter. Not all metals cut the same either. Some cut relatively clean, while others tend to cut like gum. Some grades of stainless fall into the later class while other grades of stainless (used in the nuclear reactor field) are just plain miserable to cut. But as usual, I digress.

EDM'ing and CEDM'ing should make for a smoother, more consistent bore, and represents one of those rare instances where newer is better.
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Old 07-31-2016, 12:00 PM
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To Alk8944:

Very interesting information on your discussion of EDM rifling on your Mountain Gun. Do you remember, what was the year of manufacture for the Mountain Gun you mentioned (with the 435 diameter)? Based on the dimensions you referenced, I assume this was a 44 Mag cartridge in either a 29 or 629 Mtn. Gun?

Did S&W change to EDM in 95?
It was an early 629 Mountain Gun with EDM/ECM rifling, at least 1997 as it had the new style thumb piece. When it was sold I purged it from my data-base so I can't tell you with certainty when I bought it, but not too long after 1997.

I replaced it later with a 629 "Mountain Revolver" Model 1989. It naturally has cut rifling of correct dimensions!
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Old 07-31-2016, 12:01 PM
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It sounds like Polygonal Rifling. Something Smith and Wesson learned from Walther.





Polygonal Rifling
Polygonal rifling - Wikipedia, the free encyclopedia
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Old 07-31-2016, 12:09 PM
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It sounds like Polygonal Rifling. Something Smith and Wesson learned from Walther.
It is not polygonal rifling and its use pre-dates Smith's association with Walther. It is conventional in every regard except that the transitions from groove to land are rounded rather than sharp-cornered. See Pisgah's post for exactly what ECM rifling is.

Adios,

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Old 07-31-2016, 12:21 PM
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It is not polygonal rifling and its use pre-dates Smith's association with Walther. It is conventional in every regard except that the transitions from groove to land are rounded rather than sharp-cornered. See Pisgah's post for exactly what ECM rifling is.

Adios,

Pizza Bob

Interesting! You learn something everyday on this forum.
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