S&W Flash Gap

[Michael Zeleny]

The SAAMI advises us that 0.012" is an industry maximum for revolver flash gap. Many of the pre-war Magnums that I examine for prospective purchase approach this measurement. Some of them exceed it.

As I understand their manufacture, the frames on S&W revolvers are not heat treated. Only the cylinders were claimed to be specially hardened on the Magnum revolvers. This suggests that frame stretch might be an issue. Has anyone measured their frames to check this?

What are the barrel/cylinder gaps on your pre-war S&W revolvers? I take this measurement with a Snap-On go-no go feeler gauge, on each chamber, in battery or cocked and ready to fire.

N.B.: Please do not try this trick with a 7.62 Nagant.

 

[Peter M. Eick]

I took pity on your posts all over the web and measured mine. None of the mags are over .008. The largest 38/44 is .006 the smallest is .004 of any of them.

I would guess you are looking at guns that either have been shot a lot or something happened to them. None of mine are in "pristine shape" and all but two have been fired.

Ps. Regardless of what some might say. S&W frames are heat treated. Read some the articles on the 38/44 and development of the 357 Magnum. There are references to heat treating the frame since the days of triple lock. I cannot attest this first hand since I was not there, but I have faith that it was done. Keep in mind though Roy has stated that the 38/44 and 357 Mag did not have the same heat treat.

 

[Michael Zeleny]

None of the mags are over .008. The largest 38/44 is .006 the smallest is .004 of any of them.

Thank you.

Regardless of what some might say. S&W frames are heat treated.

I am sorry for omitting my attribution for this claim. Thus spake John Linebaugh: "The frames on S&W are not heat treated thus are pretty soft." I cannot think of a better authority in this technical matter. However, I suspect that at issue here is not the heat treatment per se, but the difference between the ensuing surface and deep hardening. The only revolver that I know to use all forged and deep hardened components is the Manurhin MR-73. (Another one may be Korth.) Some of the guns chambered for Linebaugh's own cartridges use frames cast by Pine Tree Castings in 17-4PH (precipitation hardening) steel alloy containing 17% chromium and 4% nickel. These frames are also deep hardened. I am guessing that the heat treatment on forged Colt and S&W frames runs only skin deep.

 

[mete]

As far as I know the S&W, and Colt frames are not hardened .You are thinking of case hardening , they are not. 17-4PH is a stainless steel and Pine Tree Casting is part of Ruger.... The proper term is barrel-cylinder gap and this seems to have increased over the years as far as max. .004-.006" is desirable ,.012" is far too much for me !!

 

[Stainz]

I really admire John Linebaugh for his years of work in high power revolvers. However... Roy Jinks is the 'official' S&W historian - with access to all of the S&W records. He has produced scholarly works on the subject. I'll take his word as final re the 'type', and amount, of heat treating on various models.

Several calls over the years to S&W have resulted in the same 'official' range as 'acceptable' re the b/c gap - .004" - .010". I did send my 4" 625-8, bought new 9/02, back to S&W when it drug on one chamber, and only had a max gap of <.002". It had launched 8k+ rounds in steel plate challenge/plinking fare... sometimes even loosing it's cylinder when the loosened yoke screw would fall out! A hard life sent it back home for r&r at S&W 6/04 - on them - and I had it back in eight days. It was like new - with a better-than-new trigger. Of course, I don't think a registered Magnum - or .38-44 - would have that same lifetime warranty. Still, they would have the right jigs and parts...

Stainz

 

[Michael Zeleny]

As far as I know, S&W forges its revolver frames from the 4140 chrome-moly and 416 stainless alloys. Whereas 416 is air hardening, although 4140 is classified as an oil-hardening steel, in a narrow section it is air hardening. Accordingly, I am guessing that S&W performs a full-cycle anneal after forging prior to performing machining operations, because the material becomes hardened by cooling in the air. Factory literature suggests that S&W barrels and pistol slides are deep hardened, and in some instances also surface hardened. I am asking whether or not the frames are also deep hardened. My underlying interest is in finding out whether or not an S&W revolver frame is subject to plastic deformation in extended use. All of the foregoing is a product of my limited understanding uninformed by scientific insight. I am hoping for metallurgically savvy contributors to correct my interpretation.

 

[Shear_stress]

As far as I know, S&W forges its revolver frames from the 4140 chrome-moly and 416 stainless alloys. Whereas 416 is air hardening, although 4140 is classified as an oil-hardening steel, in a narrow section it is air hardening. Accordingly, I am guessing that S&W performs a full-cycle anneal after forging prior to performing machining operations, because the material becomes hardened by cooling in the air. Factory literature suggests that S&W barrels and pistol slides are deep hardened, and in some instances also surface hardened. I am asking whether or not the frames are also deep hardened. My underlying interest is in finding out whether or not an S&W revolver frame is subject to plastic deformation in extended use. All of the foregoing is a product of my limited understanding uninformed by scientific insight. I am hoping for metallurgically savvy contributors to correct my interpretation.

My understanding is that S&W parts are cold forged, so air hardening would not be an issue. The forgings are annealed to relieve residual stresses that would otherwise cause distortion during the machining operations. If necessary, the parts could then be hardened after they underwent final machining (as S&W once did with their lock work).

As to whether the frame themselves are hardened, I don't really think it's an issue within the context of "normal use". Ferrous materials have a fatigue limit, or a stress below which they can be subjected to indefinately without plastic deformation. In a nut shell, if you fire loads that never exceed the fatigue limit (whatever that may be), the frame will *never* undergo plastic deformation. The million dollar question is what that fatigue limit actually is.

Or not. For the sake of cost and weight, I'd bet dollars to cents S&W wheelguns (or any guns, for that matter) are actually designed to absorb X number of thousand rounds of ammunition loaded to SAAMI specs. This implies that the guns can happily operate above the fatigue limits of the frames, but repeated cycling at high pressures will stretch them out over time. The higher the pressures, the faster the stretching. On the other hand, if you keep your loads sane, the frames may not stretch appreciably in your lifetime.

So, the answer to your question of whether not S&W revolver frames are subject to plastic deformation after extended use is yes and/or no. There's really no way to know unless you directly consult the gun's designers. Ain't metallurgy great!

 

[Jim K]

IMHO, ALL revolver frames are subject to deformation to some extent in extended use. (In theory, a single round will cause some stretching, though miniscule.)

The amount of stretch will depend on the loads being fired. Hardness in itself has little to do with it. But is it possible to determine if the frame has stretched based solely on the b/c gap? No, it would require some very careful measurements and/or the use of special gauges to determine that.

I don't think .012" is excessive, though I prefer .006"-.007". .004" is too little and the gun will hang up from cylinder expansion if fired hot.

Jim

 

[Michael Zeleny]

IMHO, ALL revolver frames are subject to deformation to some extent in extended use. (In theory, a single round will cause some stretching, though miniscule.)

This is always true of elastic deformation. Notwithstanding the eventuality of metal fatigue, all steel deformation up to and exclusively of the yield point is reversible. The question is whether or not revolver frames operate within this envelope. Based on the data on hand, I am guessing that it is not the case for S&W N-frames.

 

[Jake H]

Hardness

Frame stretching has nothing to do with the metal's hardness. Hardness is defined as "a material's resistance to scratching".

Jake Hayes

 

[Michael Zeleny]

Frame stretching has nothing to do with the metal's hardness. Hardness is defined as "a material's resistance to scratching".

The relevant meaning of hardness is defined in the Metals Handbook as the resistance of metal to plastic deformation.

 

[Shear_stress]

The question is whether or not revolver frames operate within this envelope. Based on the data on hand, I am guessing that it is not the case for S&W N-frames.

Sorta. I tend to be cautious with what I construe as data. We really don't have much to support this statement one way or another beyond the fact that we have little anecdotal evidence to suggest that many folks have actually stretched out an N-frame.

Notwithstanding the eventuality of metal fatigue, all steel deformation up to and exclusively of the yield point is reversible.

This is true. But remember that if you cycle steel below a certain stress level, it will never fatigue. This is not the case for metals like aluminum.

 

[Michael Zeleny]

I am guessing that most centerfire guns operate above the fatigue limit and beyond the yield point of their major components. I am basing my guesses on limited personal observation of stretched frames, cracked slides, and their like. I would love to see metallurgical studies based on more representative data samples.

 

[Jake H]

Michael,

I guess we are both right about the definition of hardness. I was wrong about hardness not including plastic deformation though. When you search for the definition of hardness, you will find that there are three different principles of hardness. And two of them are scratch hardness and indentation hardness. Indentation hardness includes a material's resistance to plastic deformation.

Jake Hayes

 

[Peter M. Eick]

To a certain extent, I would argue that you have conducted your own test of fatigue limit and proven your point. The mere fact that most of the revolvers you have checked out are above the nominal (or normal) cylinder gap tells me that some stretch must have occurred. Since some revolvers like mine are lower gaps and some of the unfired ones are very tight, I would conclude from this discussion that you are looking at more heavily shot guns.

Upon a bit of reflection, heavily shot is not as correct as shot with heavy loads.

 

[Michael Zeleny]

To a certain extent, I would argue that you have conducted your own test of fatigue limit and proven your point.

Going past the fatigue limit of a given alloy would eventually result in a fracture. In the context of handguns, the best data relevant to fatigue life seems to come from the refurbishment histories of M1911 pattern pistols by U.S. armories. As regards the matter of revolver frame stretch, the relevant question is determining the yield point. I would guess that it is passed in the event of firing most centerfire rounds, but probably not with their rimfire counterparts.

Upon a bit of reflection, heavily shot is not as correct as shot with heavy loads.

The former is apt to cause failure due to fatigue fracture, whereas the latter is apt to cause wear due to plastic deformation.

 

[Jim K]

"Based on the data on hand, I am guessing that it is not the case for S&W N-frames."

Why not? Are N frames magic of some kind?

"The mere fact that most of the revolvers you have checked out are above the nominal (or normal) cylinder gap tells me that some stretch must have occurred."

Without knowing the specifications and tolerances in use when the guns were made, and without knowing exactly what the gap was when the guns were new, that statement is not supportable. I will say again, you can't judge frame stretching by the b/c gap alone.

Jim

 

[Confederate]

Warping Frames

The primary issue with full magnum ammo in medium frame guns has to do more with frame warp than gas cutting. A K-frame .357 could withstand a few thousand rounds of magnum ammo, could have a few parts changed and be back in time and ready to go. But a few thousand more rounds and the frame would warp beyond a gunsmith's ability to repair it.

Another weak area was the cylinder. The model 19/66 had cylinders that were simply too skimpy. And the cylinder notches were right over the weakest parts, which never made sense to me. To get the cylinders to close, S&W had to cut a notch out of the forcing cone, which made it subject to cracking.

Ruger sidestepped these problems by having a beefy one-piece frame which easily absorbed the blast of magnum ammo. The cylinder notches were offset so the slightly larger cylinders would hold. Finally, Ruger didn't have to cut anything off their forcing cones, but even so there were a few reported cracks of Ruger forcing cones back in the 80s.

Smith & Wesson finally introduced the 586/686 line of revolvers that addressed some of these problems, but I've often wondered why other manufacturers other than Ruger and Dan Wesson didn't go for solid-frame designs.

 

[Michael Zeleny]

"The mere fact that most of the revolvers you have checked out are above the nominal (or normal) cylinder gap tells me that some stretch must have occurred."

Without knowing the specifications and tolerances in use when the guns were made, and without knowing exactly what the gap was when the guns were new, that statement is not supportable. I will say again, you can't judge frame stretching by the b/c gap alone.

I concede that the increase in the barrel/cylinder gap in use might be attributed to cylinder shrinkage as well as it might be to frame stretching.

 

[Michael Zeleny]

The primary issue with full magnum ammo in medium frame guns has to do more with frame warp than gas cutting.

That may well be case. But frame warp appears much less likely in an N-frame than it is in a K-frame.

 

[BigG]

Tolerances

You could also get one with a short cylinder and a short bbl that would have a larger bbl-cylinder gap to begin with. This would be attributable to normal manufacturing tolerances.

What you might do is get several brand new revolvers, measure them and record all relevant measures, and shoot the heck out of them with standard known ammo, re-measuring them every x number of rounds. This would give you a set of data to work with. And we would all learn something due to your diligent pursuance of truth.

I will volunteer for some of the shooting.

 

[Michael Zeleny]

You could also get one with a short cylinder and a short bbl that would have a larger bbl-cylinder gap to begin with. This would be attributable to normal manufacturing tolerances.

Measuring many N-frame barrel/cylinder gaps beyond maximum factory specification, with no evidence of cylinder or forcing cone shrinkage, makes this attribution less plausible.

What you might do is get several brand new revolvers, measure them and record all relevant measures, and shoot the heck out of them with standard known ammo, re-measuring them every x number of rounds. This would give you a set of data to work with. And we would all learn something due to your diligent pursuance of truth.

Doubtless that would be the best way to do it. But I was hoping for some wisdom of the ages to make up for my want of diligence.

 

[unspellable]

Excess cylinder gap

If a S&W revolver left the factory with a proper cylinder gap and over time has developed excessive cylinder gap, the first thing to suspect is not frame stretch but ratchet wear, possibly combined with wear at the point where the ratchet bears on the frame. This would result in losing headspace by about the same amount cylinder gap has increased. The yoke tail and rachet locate the cylinder fore and aft and are the weak points in the S&W design.

 

[Michael Zeleny]

If a S&W revolver left the factory with a proper cylinder gap and over time has developed excessive cylinder gap, the first thing to suspect is not frame stretch but ratchet wear, possibly combined with wear at the point where the ratchet bears on the frame. This would result in losing headspace by about the same amount cylinder gap has increased. The yoke tail and rachet locate the cylinder fore and aft and are the weak points in the S&W design.

This is a helpful observation. To follow up, what sort of service can remedy this condition on a S&W revolver? How do other swingout cylinder revolver designs locate the cylinder in the frame?

 

[unspellable]

Methods and Corrections

I am going to restrict this to conventional single action solid frame revolvers and conventional swing out cylinder double action revolvers. In both types the rearward movement of the cylinder is limited by the ratchet bearing against the frame. Wear at this point will be influenced by the actual bearing surface and the metallurgy involved. Single actions will typically have more bearing surface than double actions. The double action ratchet must accommodate two modes of operation with differing hand movements in the two modes.

In most double action revolvers, correcting this requires fitting a new ratchet which is generally one piece with the extractor star.

In most single action revolvers the forward travel is limited by the cylinder neck bearing against the frame. The is room here for an ample bearing surface. Most single actions are quite strong in this regard.

Double action revolvers vary in the method of limiting forward travel. In the S&W the tail of the yoke tube bears against the bottom of the cylinder well. There is a rather small bearing surface and so the S&W is more subject to wear than some other revolvers. There are two methods of correcting wear. One is to stretch the yoke tube (S&W’s factory method.) by impressing a groove in it with a device similar to a tubing cutter. The other method is to add spacing shims at the bottom of the cylinder well. In both cases, if the problem is due to wear the yoke tube tail and the bottom of the cylinder well must be dressed up to restore flat surfaces. Typically the S&W will loosen up at the yoke tube tail/cylinder well bottom interface faster than at the ratchet/frame interface.

In a Colt the forward travel is limited by the cylinder neck bearing on the yoke collar which provides more surface than in a S&W. This results in slower wear. Unfortunately the older type Colt action’s timing is more sensitive to end shake than the S&W. The hand and ratchet interface is the weak point in the older Colt action and requires closer fitting than in a S&W. Newer Colts have a hand and ratchet more along the lines of other revolvers. The Python was the last Colt made with the old action.

Once the cylinder is properly fitted, the cylinder gap is adjusted by grinding or filing off the rear of the barrel. If the gap is too large, the barrel must have its shoulder machined down and be set back a thread or a new barrel fitted. The exception here is the Dan Wesson which has an adjustable cylinder gap.

In single actions, excessive play at either end is corrected by fitting a new cylinder. Fortunately, single actions, if correctly fitted to begin with tend to stay that way. A replacement cylinder should be a bit long in both ratchet and neck to allow for the removal of a bit of metal in fitting.