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Old 08-16-2020, 05:33 PM
Hiram Jr Hiram Jr is offline
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Hi guys,

Thought I'd glean some wisdom and knowledge here before I do something stupid, I just measured my b/c dimension and endshake:


B/C gap:
.006" in forward position
.0115"-.012" (a guesstimate; .012" gauge pretty snug) in rearward position


Endshake: .006"


My questions, should I, or could I, send .357 Magnum rounds through her at all? Just got the gun yesterday, and am pretty disappointed with that endshake number. Also, do you recommend an immediate fix. Have never attempted a washer job thus far. Would sending it back to Smith & Wesson be wise?

Please advise.
Thanks!
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Old 08-16-2020, 06:10 PM
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Get some endshake washers, they come in .002 and .004 thickness. Add a ..004 and recheck ..
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Old 08-16-2020, 06:13 PM
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You can shoot magnums as is. But I’d eventually fix it. Easy to do.
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Old 08-16-2020, 07:18 PM
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endshake shims are an easy job...I think "Triggershims" is who I buy them from...can even watch video if it makes you feel better...have maintained a few this way...don't be mad it's a maintenance deal!
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Old 08-16-2020, 07:32 PM
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Any way to do it without a bench vice?
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Old 08-16-2020, 07:37 PM
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Keep in mind that if you shim the cylinder back on the yoke .004", your B/C gap will then be .010". Perhaps a .002" shim would be better. That would keep your headspace in spec, and your B/C gap would be .008".

The bottom line is, don't sweat the "end shake" if your front and rear specs are correct.
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Old 08-16-2020, 07:56 PM
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Quote:
Originally Posted by armorer951 View Post
Keep in mind that if you shim the yoke back .004", your B/C gap will be .010". Perhaps a .002" shim would be better. That would keep your headspace in spec, and your B/C gap would be .008".

Don't sweat the "end shake" if your front and rear specs are correct.
Thanks! I was concerned about the resulting b/c gap.
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Old 08-16-2020, 10:21 PM
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One more novice question. Is actual b/c the gap caused when pushing the cylinder back toward the recoil shield, or fore towards the barrel?
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Old 08-16-2020, 10:29 PM
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The B/C gap measurement is the gap when the cylinder is at rest....toward the front.
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Old 08-19-2020, 08:21 AM
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Quote:
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The B/C gap measurement is the gap when the cylinder is at rest....toward the front.
That is correct. Reference the classic text “ pistolsmithing” by Major George Nonte. Place fire cases in cylinder and place a feeler gauge up to about .008 between cases and recoil shield To where it is a snug fit.. (This measures and accounts for normal headspace. If greater than .008 headspace may be a little too much). With rear feeler gauge in place, measure barrel cylinder gap. This is the true effective gap. Simply pushing Empty cylinder back leaves no allowance for headspace and endshake. Well described in text I referenced.
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Old 08-19-2020, 09:25 AM
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Then end shake shims do not require a vice. Just something that will grasp the end to the ejector rod without damaging it or its finish. A drill chuck works well. Just tighten it on rod and use it to hold onto while ytou unscrew the cylinder. Remember to stick at least 3 fires cases in cylinder and that it is left hand thread.


Adjusting the endshake to .004 leaves me with a thought. I cock the revolver and pull the trigger, hammer goes forward and hammer nose goes though frame at bushing and strikes the primer driving it, the case and the cylinder forward. Ignition and initial explosion now occurs with minimum B/C gap. But, then things happen fast. the case is slammed back against recoil shield and bullet exits case passing into throat and forcing cone.

Does the cylinder remain forward at this point with minimum B/C gap or does the expanded case take the cylinder with it as it recoils back into shield. My belief is that the cylinder will move back with case, slamming center of ratchet into frame and opening up the B/C gap to its max as the base of bullet exits cylinder and hot gasses escape thru B/C gap with cylinder as far to rear as possible. OR does the case slam back before it can drag back the cylinder leaving it remain forward with minimum B/C gap at this point?

I always set my gap to .002 or under. as long as I still have necessary head space between case head and recoil shield.
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Old 08-19-2020, 10:33 AM
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During recoil, and under the strong recoil forces being exerted on the frame, to which the yoke is attached, the cylinder remains pressed forward on the yoke barrel. The cylinder itself is "free floating" within the gauge limits provided by the assembly on the yoke when fully assembled, and although it must follow the frame's rearward movement, it does so while in contact with the bearing surface at the end of the yoke barrel.

These recoil forces exerted during detonation are the primary cause of the peening that occurs on the end of the barrel of the yoke. Over time and usage, this results in the development of the oftentimes dreaded "end shake" in the assembly.
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Old 08-19-2020, 11:42 AM
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Then end shake shims do not require a vice.
My grammar OCD requires me to note that a "vice" is a weakness of character or behavior, such as the irresistible urge to tinker with your revolvers; whereas, a "vise" is the device you use to hold your revolver in place while you engage in your vice.
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Old 08-19-2020, 08:23 PM
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Originally Posted by armorer951 View Post
During recoil, and under the strong recoil forces being exerted on the frame, the cylinder remains pressed forward on the yoke barrel. The cylinder itself is "free floating" within the gauge limits provided by the assembly on the yoke when fully assembled, and although it must follow the frame's rearward movement, it does so while in contact with the bearing surface at the end of the yoke barrel.

These recoil forces exerted during detonation are the primary cause of the peening that occurs on the end of the barrel of the yoke that, over time and usage, results in the development of the oftentimes dreaded "end shake" in the assembly.
I see the logic now. The frame is recoiling back faster than the cylinder and the B/C gap stays at minimum. Had never thought that all out before. Jim
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Old 08-19-2020, 09:49 PM
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But wait. I can understand that the yoke tube being peened causing it to become shorter. But, this would allow the cylinder to move forward. It would not cause the cylinder to be moved back and give a large B/C gap


If a gun started off with .005 gap when held back and .004 when pressed forward, for .001 endshake, which would be nice. Then was fired with stout loads a lot, the yoke tube would be peened by the cylinder movement under recoil. The cylinder itself remains the same length. The barrel extension remains the same length. To develop endshake by the yoke tube is peened shorter would allow the cylinder to move forward on yoke when checked for endshake. If cylinder was peened .003 shorter then the forward check would be .002 and the rear ward would be the same .006 it was to start. Why do guns develop larger gaps then? Frame stretching, the barrel extension face being eaten away, or the ratchet face being worn down are the only ways. Length of cylinder with ratchet, plus barrel extension subtracted from frame window. You can check max B/C gap without the cylinder even being mounted on a yoke.

If the frame window remains the same, the length of the cylinder itself remains the same and the barrel extension remains the same the maximum the maximum barrel to cylinder gap remains the same, no mater the length of the yoke tube. A super short tube can only allow the cylinder to move forward until it contacts the barrel and it has no control over minimum rear gauge. That is a function of the center of ratchet.

It would be interesting to take a new 357. Measure the frame window, yoke tube, barrel extension, ratchet height, cylinder length, endshake and B/C gap. then fire 10,000 rounds, check them all again, then fire another 10,000 and recheck and see exactly what happens. Developing a larger B/C has to be either frame stretching or flame blast slowly cutting off the face of the barrel extension.

As it is I just fix the shake, make sure my rear gauge is good, if the gap is to big either turn the barrel back or stick it in the safe and go on to another project. I have a sloppy pre 28, I have never fixed, but I see it being a big bore with another barrel someday anyway.

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Old 08-19-2020, 10:21 PM
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Think of the cylinder as an assembly with components that ride both on, and in the yoke barrel. As this inevitable peening and wear to the end of the yoke barrel occurs during firing and usage, the cylinder assembly moves forward on the yoke because the yoke barrel becomes shorter. You can also factor in a bit of wear and tear and peening on the bearing surface inside the cylinder cavity, which the end of the yoke barrel bears against during both rotation and recoil. This normal wear inevitably results in a smaller B/C gap, and a larger headspace....or "rear gauge" as S&W calls it. The headspace at the rear of the cylinder grows larger in proportion to the front gauge getting tighter (smaller) as this wear takes place.

If the rear gauge on a particular revolver is .012" and the B/C gap is .005" to start, and with .001" of end shake provided during fitting, after 10,000 hypothetical rounds of firing, lets say the end shake has opened to .004". In this revolver then, the B/C gap with the cylinder at rest would now be .001" and the rear gauge or headspace would have opened to .016" or thereabouts, and would be close to being out of specification. (typical magnum recessed cylinder)

Technically, the "end shake" we are feeling and measuring in the cylinder assembly when it is it is installed in the frame (cylinder closed) is the open or "unfilled" distance (space) between the components in the cylinder assembly that are situated between the breechface and the end of the yoke barrel.
If there is open gauge or what we typically refer to as "end shake", that's where it is.
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Old 08-20-2020, 06:42 AM
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Yes, I agree. But, what I want to know is how does a gun develop an excess amount of B/C gap? Or if it exists was it always there?
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Old 08-20-2020, 08:03 AM
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I've never seen a B/C gap get larger, except by shimming or swaging the yoke barrel, which results in moving the cylinder back on the yoke. I guess it would be possible for the barrel extension to exhibit wear due to erosion from firing, but I have never experienced this or seen this happen.
If the front gauge is too large the gap was fit improperly at the factory.
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Old 08-20-2020, 08:28 AM
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i have always wondered about this. Keep seeing people posting endshake and large gaps. Except for the one Highway patrolman I have all mine have decent gaps. I am not that worried about it anyway. If need be I can fix a big gap and fixing endshake is easy.

I was just thinking and wondering. Thanks for tthe discussion. Jim
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Old 08-20-2020, 08:43 AM
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I'd fix it now. Not because it's all that bad you can't shoot it. Because I like things to be right. It will only get more expensive and more difficult to get it fixed as time goes by.

I did with my 66. 25,000+ rounds of mid-range .38 loads later it's still tight.
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Old 08-20-2020, 05:51 PM
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Quote:
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Then end shake shims do not require a vice. Just something that will grasp the end to the ejector rod without damaging it or its finish. A drill chuck works well. Just tighten it on rod and use it to hold onto while ytou unscrew the cylinder. Remember to stick at least 3 fires cases in cylinder and that it is left hand thread.


Adjusting the endshake to .004 leaves me with a thought. I cock the revolver and pull the trigger, hammer goes forward and hammer nose goes though frame at bushing and strikes the primer driving it, the case and the cylinder forward. Ignition and initial explosion now occurs with minimum B/C gap. But, then things happen fast. the case is slammed back against recoil shield and bullet exits case passing into throat and forcing cone.

Does the cylinder remain forward at this point with minimum B/C gap or does the expanded case take the cylinder with it as it recoils back into shield. My belief is that the cylinder will move back with case, slamming center of ratchet into frame and opening up the B/C gap to its max as the base of bullet exits cylinder and hot gasses escape thru B/C gap with cylinder as far to rear as possible. OR does the case slam back before it can drag back the cylinder leaving it remain forward with minimum B/C gap at this point?

I always set my gap to .002 or under. as long as I still have necessary head space between case head and recoil shield.
Drill chuck, brilliant. Thank you!
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Old 08-20-2020, 06:01 PM
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Do recessed chambers in the cylinder render the necessity of measuring headspace with spent casings moot?
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Old 08-20-2020, 06:04 PM
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Quote:
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My grammar OCD requires me to note that a "vice" is a weakness of character or behavior, such as the irresistible urge to tinker with your revolvers; whereas, a "vise" is the device you use to hold your revolver in place while you engage in your vice.
Absolutely correct. Thank you for catching that. Using proper grammar is good advice!

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Old 08-21-2020, 08:27 PM
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Quote:
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Do recessed chambers in the cylinder render the necessity of measuring headspace with spent casings moot?
S&W armorers were taught to measure headspace without casings in the cylinder chambers. (after a good cleaning and wipe down)

Correct headspace for your 19-3 would be .012" - .018". (specs dated 10-1984)
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Old 08-23-2020, 07:01 PM
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S&W armorers were taught to measure headspace without casings in the cylinder chambers. (after a good cleaning and wipe down)

Correct headspace for your 19-3 would be .012" - .018". (specs dated 10-1984)

That's good news. Thank you!
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Old 08-24-2020, 04:04 AM
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I'd want to fix the excessive endshake before firing any more magnum loads.

It would seem to me the excessive play will only cause the cylinder to batter the yoke's barrel even more.

Fix it first, it's an easy job.

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Old 08-24-2020, 09:14 PM
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I have installed end shake shims on a few revolvers, but not a lot of them. And my experience from a small number of attempts, is that sometimes the end shake shims are very straightforward to install, and other times not so much.

In particular, I have experienced two problems.

The first problem is that the bottom of the cylinder, where the shim sits, may have been peened by the yoke until the surface is far from flat. I have seen some instructions which suggested that this surface should always be trued up with an end mill in a milling machine. My usual method is to install a shim and then check that it has reduced the end shake by the expected amount. If a .002 shim reduces end shake by .002, then it is probably sitting flat enough. However, on one occasion, I installed a .002 shim in a gun with .007 end shake, and it bound up the cylinder. So clearly, something was nowhere close to flat. I have been told that if the shims do not sit flat, then they can tear and bind the cylinder, but I do not know if this is true or myth.

The other problem I have experienced is having severe run out in the ejector rod after disassembling and reassembling the cylinder assembly. I believe this happens because the threads for the ejector rod are not quite cut on a true center. So even though the ejector rod is perfectly straight, it does not spin true after it is tightened into the cylinder. For some cylinders the ejector rod seems to develop run out every time it is loosened and retightened. There is a jig for truing the ejector rod after it is tightened into the cylinder, but this jig is not available to the average home smith.

So overall, I do think adding end shake shims is usually pretty easy, and it is a common task for the home gunsmith. But I do like to offer some warning that it does not always go easily.
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Old 08-26-2020, 06:21 PM
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Originally Posted by lefty_jake View Post
I have installed end shake shims on a few revolvers, but not a lot of them. And my experience from a small number of attempts, is that sometimes the end shake shims are very straightforward to install, and other times not so much.

In particular, I have experienced two problems.

The first problem is that the bottom of the cylinder, where the shim sits, may have been peened by the yoke until the surface is far from flat. I have seen some instructions which suggested that this surface should always be trued up with an end mill in a milling machine. My usual method is to install a shim and then check that it has reduced the end shake by the expected amount. If a .002 shim reduces end shake by .002, then it is probably sitting flat enough. However, on one occasion, I installed a .002 shim in a gun with .007 end shake, and it bound up the cylinder. So clearly, something was nowhere close to flat. I have been told that if the shims do not sit flat, then they can tear and bind the cylinder, but I do not know if this is true or myth.

The other problem I have experienced is having severe run out in the ejector rod after disassembling and reassembling the cylinder assembly. I believe this happens because the threads for the ejector rod are not quite cut on a true center. So even though the ejector rod is perfectly straight, it does not spin true after it is tightened into the cylinder. For some cylinders the ejector rod seems to develop run out every time it is loosened and retightened. There is a jig for truing the ejector rod after it is tightened into the cylinder, but this jig is not available to the average home smith.

So overall, I do think adding end shake shims is usually pretty easy, and it is a common task for the home gunsmith. But I do like to offer some warning that it does not always go easily.

Thank you, Lefty. To be honest, I might send it to S&W, and have them fix the endshake and tune it up. I acquired it in a trade. The snubby I traded for it was a gun that was given to me, so as of now, I have zero invested in it. Would you know if S&W works on revolvers 50+ years of age?
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Old 09-12-2020, 10:20 PM
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There's some pretty well-reasoned disagreement on the cylinder position as a round is fired. If you go to rugerforum.net and search "Revolver Recoil Physics", and thehighroad.org and search "Barrel to cylinder gap and endshake.", you'll find the claim that the once the bullet is free of the cylinder the cylinder moves fully back. The thread on thehighroad has a supporting video.
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Old 09-13-2020, 05:44 PM
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By Iowegan:

"When the base of the bullet passes the B/C gap, there is a radical change. Because the case has expanded and is now held tight against the chamber walls, the cylinder will be thrust to the rear until it is stopped when the ratchet surface contacts the recoil shield."
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Old 09-14-2020, 02:04 AM
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The case is forced out of the chamber back against the breech plate which causes the primer to be pushed back into the primer pocket.

Otherwise every time you fired a round in a revolver the cylinder would bind up, just like what happens when you fire a "primer only" round because:

-the primer's pressure forces it out of the pocket (because the primer pocket's flash hole restricts the pressure) & it stays out, against the breech plate because there was no powder charge to force the case back into the breech plate resetting the primer back into the pocket, flattening it, & putting the tell-tale "forensic" marks on it from the breech plate's imperfections.

.

The cylinder is essentially "floating" on the yoke's barrel.

The yoke's barrel gets pounded, & flattened, (causing excessive clearance & endshake) not by the cylinder (& rachet face) being forced rearward against the breech plate (which is away from the end of the yoke barrel) but by the frame of the revolver recoiling rearwards pounding the attached yoke's barrel into the the cylinder's innards.

The cylinder being harder wins, the end of the yoke's barrel being softer loses.

.
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Old 09-14-2020, 06:49 AM
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This forum is amazing!
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Old 10-01-2020, 10:14 PM
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Power Custom makes a tool to check and straighten ejector rod runout. You can get it from Brownells. Power custom also makes yoke and cylinder shims for endshake correction.
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Old 10-01-2020, 10:17 PM
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Has anyone looked at B/C gap on new S&W revolvers lately. I swear they are 12-15 thousands just based on visual check. I looked at several 686's and even a couple of Performance Center 686's yesterday and was shocked at the gap.
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Old 10-02-2020, 08:08 AM
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Has anyone looked at B/C gap on new S&W revolvers lately. I swear they are 12-15 thousands just based on visual check. I looked at several 686's and even a couple of Performance Center 686's yesterday and was shocked at the gap.
Back in the day, the maximum that S&W allowed was 0.008", but today their maximum spec is 0.012".
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Old 10-07-2020, 03:37 PM
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During recoil, and under the strong recoil forces being exerted on the frame, to which the yoke is attached, the cylinder remains pressed forward on the yoke barrel. The cylinder itself is "free floating" within the gauge limits provided by the assembly on the yoke when fully assembled, and although it must follow the frame's rearward movement, it does so while in contact with the bearing surface at the end of the yoke barrel.

These recoil forces exerted during detonation are the primary cause of the peening that occurs on the end of the barrel of the yoke. Over time and usage, this results in the development of the oftentimes dreaded "end shake" in the assembly.
If I understand your post correctly, the cylinder is as far forward as it can go as the bullet moves from the cartridge to exiting the gun.

If this is correct, removing endshake shims, to allow the cylinder to move further forward, would close the b-c gap, increasing bullet speed.

Am I missing something here?

I can test this pretty easily; I could chrono one of my revolvers with shims, remove them, and chrono again.

Not sure if this is worth the effort, any opinions?
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Old 10-07-2020, 03:48 PM
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What you're missing is if you remove the shims, the cylinder moves forward by that amount, and now your headspace or "rear gage" as S&W calls it, is potentially out of spec. This can cause reliability problems, and issues with proper carry up of the cylinder.

The critically important thing is for the front and rear gages to be in spec. If they are, then the end shake that is present is a non-issue.

I would expect any gains in velocity would be negligible, probably not even measurable.
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Old 10-07-2020, 04:49 PM
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Originally Posted by armorer951 View Post
What you're missing is if you remove the shims, the cylinder moves forward by that amount, and now your headspace or "rear gage" as S&W calls it, is potentially out of spec. This can cause reliability problems, and issues with proper carry up of the cylinder.

The critically important thing is for the front and rear gages to be in spec. If they are, then the end shake that is present is a non-issue.

I would expect any gains in velocity would be negligible, probably not even measurable.
I'm not planning to leave the revolver with lots of endshake, just remove the shims to test your belief that the cylinder is as far forward as it can go as the bullet moves out of the gun.

Why would you expect velocity gains to be negligible? If the cylinder gap is smaller, shouldn't the bullet go faster? If your posts are correct, a revolver with a 0.008" b-c gap and 0.004" of shims would have an effective gap of 0.004" with the shims removed. Shouldn't that make the bullet faster?

I've always thought (and read at at least a couple of places) that the cylinder is all the way back after the bullet leaves the cylinder. I'm just trying to understand your posts, and verify them if possible.
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Old 10-07-2020, 05:36 PM
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I'm an old guy so I'm probably wrong.

I base my opinion with regards to the position of the cylinder during the millisecond period immediately following ignition on physics.

My opinion about the the growth of what we all call "end shake" has been formed by observing and repairing the damage that inevitably occurs to the end of the barrel of the yoke while working as an armorer over the last 40+ years. This peening (shortening) of the yoke happens during heavy recoil....there's really no other way the damage can occur. This gage, or space between components (the end of the yoke and the bearing surface inside the cylinder cavity) will grow from use. That's a very hostile environment in there, and the damage creates not only stress for revolver owners, but a market for toolmakers and the folks who sell yoke shims.

And, you are correct, the shell casing is pressed all the way back in the cylinder under considerable pressure at some point during ignition, otherwise, we would not see breach markings (tool marks) created by the high pressures on the primers and casings.

Perhaps you are also correct about the wider B/C gap causing a loss in velocity, I just don't know. With the standard deviation and variables in hand-loaded and factory ammunition, I would think it would be nearly impossible to verify or quantify such a small, negligible loss of velocity using a chronograph.

I do admire your curiosity and your desire to ask questions. That's how we all learn about these mechanisms.
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Old 10-07-2020, 06:31 PM
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Fellas,
I’m an old retired LE firearms instructor and attended the S@W factory armorer school in 1987. I took care of a 23 man department’s guns for a few years before we went to Glocks . Then did two Glock armorers schools. I still know my way around a S@W revolver and do and action job here and there.

Long story short, Armorer951 knows his stuff. Shut up and listen to him. ��
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Old 10-07-2020, 10:16 PM
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Quote:
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I'm an old guy so I'm probably wrong.

I base my opinion with regards to the position of the cylinder during the millisecond period immediately following ignition on physics.

My opinion about the the growth of what we all call "end shake" has been formed by observing and repairing the damage that inevitably occurs to the end of the barrel of the yoke while working as an armorer over the last 40+ years. This peening (shortening) of the yoke happens during heavy recoil....there's really no other way the damage can occur. This gage, or space between components (the end of the yoke and the bearing surface inside the cylinder cavity) will grow from use. That's a very hostile environment in there, and the damage creates not only stress for revolver owners, but a market for toolmakers and the folks who sell yoke shims.

And, you are correct, the shell casing is pressed all the way back in the cylinder under considerable pressure at some point during ignition, otherwise, we would not see breach markings (tool marks) created by the high pressures on the primers and casings.

Perhaps you are also correct about the wider B/C gap causing a loss in velocity, I just don't know. With the standard deviation and variables in hand-loaded and factory ammunition, I would think it would be nearly impossible to verify or quantify such a small, negligible loss of velocity using a chronograph.

I do admire your curiosity and your desire to ask questions. That's how we all learn about these mechanisms.
I've always tried to figure things out when there are competing explanations.

This place BBTI - Ballistics by the Inch :: Cylinder Gap has some really interesting measurements on b-c gap vs velocity.

I think the big difference between what you and other authorities say is that they attribute yoke peening primarily to the forward motion of the cylinder slamming onto the yoke as the bullet goes through the throat, whereas you attribute it to the frame (and yoke) slamming back into the cylinder during recoil. There's got to be some really good super fast video somewhere.

You may be an old guy, but I always read, and enjoy your posts, and you are almost always right.
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  #42  
Old 10-08-2020, 09:31 AM
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"Almost always"....proof of that is in post #41. Looks like the data shows the difference is measurable. Would this minuscule difference have any impact (pardon the pun) on terminal ballistics performance of the projectile? Not really.

Very interesting data. Looks like the margin or difference in terms of velocity is harder to define when loads are tested out of shorter barrels. I'm wondering how or if they were able to "figure in" or account for the inevitable inconsistency in terms of the loadings themselves?

Perhaps this proves we're not actually crazy, if we are curious about the same things that these people who did the testing are curious about. I hope so. (I know my wife thinks I am)
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Old 10-08-2020, 10:22 PM
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I had a .445 SuperMag Dan Wesson a long time ago, and I remember running the b-c gap very tight in my quest to get a 180 grain bullet over 2000fps. I normally had it around 0.003" on the chamber with the smallest gap. On my speed quest I had it very close to touching on that chamber, and I used that one for the chrono. It helped, but not as much as I had hoped. I wish I could find my notes.
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