Can this be more than one way to skin a cat?


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hang fire
January 18, 2012, 09:29 AM
On my 1st generation black powder frame Colt 1873 SA I have excessive barrel/cylinder face gap. At first when checked, thought it was 0.012”, but on closer examination it proved to be 0.015”.

From what I have read and been told, the basic fix is to remove the barrel, face off barrel at thread diameter and recut one or more threads, reinstall the barrel, if required face off the barrel to correct clearance and re-cone.

As this Colt was mfg. in 1886, I do not want to do any permanent modification as that would lower the collector value.

As I understand the physics, upon firing, the primer extrudes to the rear and pressure immediately increases in the cartridge case. As pressure builds, the cartridge case moves to the rear, reseating the primer and the cartridge case expands, conforms to, and grips the chamber walls. As the bullet passes into the chamber throat, the cylinder moves forward with the bullet, stopping when the cylinder base pin bushing gas ring contacts the forward frame face. When the bullet leaves the chamber throat and enters the barrel forcing cone, a rapid change of pressure forces transpires. The pressure now forces the cylinder rapidly to the rear and the cylinder ratchet comes to bear forcefully upon the recoil shield.


http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P1010329.jpg

http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P1010327.jpg

The barrel/cylinder face gap at this point is now at its maximum limits.

One can buy or make shims for the cylinder pin bushing to reduce cylinder end shake (AKA destructive battering ram) clearance, this sets the cylinder back, but does nothing to remedy the excessive barrel/cylinder face gap.

I am thinking of making a form fitted recoil shield shim of the correct thickness (0.008”) to reduce the barrel/cylinder face gap to 0.007”. As these are modern solid head cartridge cases, I do not think 0.008” will create a problem with BP pressures. As the shim will be form fitted into recoil shield recess, there will be no movement of it and will be further retained by the base pin. Shim stock can be purchased in precise thickness and of tempered steel. Once the shim fits correctly, a transfer punch of the correct diameter through the front base pin hole can mark for the hole location.

The shim would be form fitted cut as per the masking tape example here.

http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P1010331.jpg

I am not an engineer, nor stayed at a Holiday Inn last night, so any input and critique as to my approach would be appreciated.

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Old Fuff
January 18, 2012, 10:19 AM
Given the considerable value of the piece, I would re-think this whole business.

First of all, the barre/cylinder gap in revolvers was usually much larger then in modern revolvers. This is because black powder fouling could build up and eventually make the cylinder difficult if not impossible to turn. If you are not getting excessive side spitting at the gap I wouldn't worry about it.

If any work is going to be done I would place it in the hands of a professional, who is both experienced in restoring these revolvers, and has the tools to do it correctly. I suggest David Chicoine at www.oldwestgunsmith.com

If called for, he can set the barrel back, and adjust the length of the ejector tube to match (which is so far something you haven't thought of). He can do this in a manner which will have no negative affect on the collector's value.

Shooting the revolver using modern smokeless powder ammunition is questionable in itself, but if you decide to do it, it would be wise to have a new cylinder fitted to the gun while making no alterations to the frame. If You want to go in this direction M. Chicoine can take care of it. You can return the original cylinder to the gun for display purposes.

You also might consider that the total cost (including a new cylinder) of doing all this might come close to, or exceed the price of a new Colt SAA clone (roughly $500.00 new, $300.00 up used) in which case you could retire your old six-shooter and shoot a much safer gun.

velocette
January 18, 2012, 10:26 AM
Old Fuff has offered some really good advice. I respectfully suggest that you listen to his words of wisdom.

Roger

hang fire
January 18, 2012, 11:48 AM
Given the considerable value of the piece, I would re-think this whole business.

First of all, the barre/cylinder gap in revolvers was usually much larger then in modern revolvers. This is because black powder fouling could build up and eventually make the cylinder difficult if not impossible to turn. If you are not getting excessive side spitting at the gap I wouldn't worry about it.

If any work is going to be done I would place it in the hands of a professional, who is both experienced in restoring these revolvers, and has the tools to do it correctly. I suggest David Chicoine at www.oldwestgunsmith.com

If called for, he can set the barrel back, and adjust the length of the ejector tube to match (which is so far something you haven't thought of). He can do this in a manner which will have no negative affect on the collector's value.

Shooting the revolver using modern smokeless powder ammunition is questionable in itself, but if you decide to do it, it would be wise to have a new cylinder fitted to the gun while making no alterations to the frame. If You want to go in this direction M. Chicoine can take care of it. You can return the original cylinder to the gun for display purposes.

You also might consider that the total cost (including a new cylinder) of doing all this might come close to, or exceed the price of a new Colt SAA clone (roughly $500.00 new, $300.00 up used) in which case you could retire your old six-shooter and shoot a much safer gun.


Thanks for your reply Old Fuff.

There will be no permanent modification whatsoever of the revolver. The fitted recoil shield shim would merely be secured in place by the base pin and cylinder ratchet bearing upon it and could be taken out instantly when cylinder is removed.


Well aware of the BP fouling, consequences of it and as to why BP revolvers need more barrel/cylinder face clearance than smokeless revolvers.

Not sure I understand comment as to the ejector tube? Why would it have to be shortened, no modification would have taken place which would necessitate it?

I will not even consider having the firearm altered or worked on which would permanently modify or change from the original as per the Colt letter I have on it. The revolver, which aside form the excessive B/C gap, is in very good mechanical condition and locks up tight. It will seldom be fired and when done so, only with the holy black, no smokeless or BP subs, period.

Old Fuff
January 18, 2012, 06:12 PM
1. It may or may not be consequential, but your shim at the back will move the cylinder forward, and may create a headspace problem, It will also move the cartridge head and primer away from the firing pin.

2. If you should have the barrel set back to shorten the excessive gap, you would also move the lug in the barrel into which the ejector tube screw is threaded. If you move the barrel backwards the ejector tube has to be moved the same distance if the screw is going to still go into the lug. The gunsmith I mentioned (David Chicoine) has a national reputation in the field of restoring "Wild West" guns, and has the experience and tooling to do a job that's so good it would go undetected.

3. You may be surprised to learn that you can do serious damage while using black powder and/or a BP substitute, and you can do it with no more then one shot. Why so?

While the Colt Company always used the best materials they could get at the time, the steel was a far cry from what is available now vs. the middle 1880's. Cylinders were made out of round bar stock, that was made in open-hearth furnaces and impurities could get into the metal. They also sometimes had seams that would in time weaken whatever was made from it. Cylinders were not heat treated, nor were the revolvers proof fired.

While the risk of cracking a cylinder in your over 125 year-old revolver is improbable, it's far from impossible. In any case the chance can be reduced to zero if you have a modern "shooting cylinder" fitted to the gun. Any fitting is done to the cylinder, not the rest of the revolver - which remains as it is. If or when you desire, you can exchange the cylinders and return the original one.

There is a remote chance that you might crack the barrel at the rear, in the forcing cone. Again, all it takes is one shot. Once serious damage is done you may find that it can't be repaired, or if it can the work will be expensive, and at best the gun devalued. The only question is, "by how much."

I stand by my advice that the best course would be to retire the old gun, and shoot a modern reproduction, which for all practical purposes would be identical. Such a reproduction, exact in every detail, can be found at www.cimarron-firearms.com for about $500.

I am also aware that not a whole lot of folks ever take my advice. For a second opinion I suggest you contact Mr. Chicoine, who can tell you some real horror stories.

col.lemat
January 18, 2012, 06:40 PM
.015 is towards the upper limit for Barretl to cylinder gap. It would be OK for ocaisonal shooting say a cylinder or two on the holidays, but with the time spent cleaning afterwords would it be worth it? You would be better off retireing it and buying a new made colt BP gun. Your idea of the shim would take up the excess gap, but relocates it to the cartridge base & recoil shield. So still not a perminent soluition. There is another way of fixing that was not mentioned but the cost is about the same as setting the barrel back which equils the cost of a new manufractured gun as already mentioned. My self I would retire it to very special celebrations only.

rbernie
January 18, 2012, 08:29 PM
I am also aware that not a whole lot of folks ever take my advice.And, in matters such as these, that would be their loss.

rcmodel
January 18, 2012, 08:33 PM
I am also aware that not a whole lot of folks ever take my advice.

Well, I certainly always do.

Sometimes!!! :D

rc

Old Fuff
January 18, 2012, 11:17 PM
Well now! I seem to have some support in high places... Maybe I should run for President... :D

hang fire
January 19, 2012, 02:04 AM
I will preface this post by stating this is only what I did. And in no way imply or recommend the procedure for others to copy or do likewise.

Got a 0.009” recoil shield shim made up and installed, works like a charm, fired 25 rounds and the steel shim is not even marked by the cylinder ratchet. After firing and cleaning, the barrel/cylinder gap is now 0.005” I had to make up three shims before getting one of right thickness, fitted right where it was held captive in the recoil shield recess with no movement and base pin hole lined up. But was no big deal as they were easy to make.

As the thin shim stock cut so easy with a pair of heavy scissors. Found it best to just sandwich strip of shim stock between two pieces of clamped hardwood and drill for a clean hole. (could have used hand power punch for same) Rough cut the shim stock to size, put it on inserted base pin, then fitted and trimmed with scissors for precise fit in recoil shield recess.

Had to remove three 0.002” cylinder base pin bushing bearings (read as shims, Brownells calls them Endshake Bearings) to obtain 0.002” cylinder end play. The bearing/shims are nice for correcting excessive endshake, (or in my case, removing to obtain cylinder end play) saves having to buy and fit a new cylinder base pin bushing on 1st and 2nd gen Colt 1873 SA or clones that have the removable bushing.

I note some have expressed concern about the 0.009” shim creating excessive head space or other problems. Set a mike or caliper to 0.009” to see how little it really is, or, mike the thickness of a fingernail for a comparative value. After all, we are talking revolvers, where the solid head cartridge cases are free to move back and forth in the chambers for clearance and the cylinder to rotate.

Ever take a look at a chambered round in some rather high pressure locked breech semi automatic pistols? I have seen pistols where a goodly portion of the case head is totally unsupported by the chamber to considerable depth.

1911Tuner
January 19, 2012, 08:58 AM
Got a 0.009” recoil shield shim made up and installed, works like a charm, fired 25 rounds and the steel shim is not even marked by the cylinder ratchet.

Why would it be? The cylinder is never driven backward, nor can it be pulled backward with any significant force by the case. When the bullet hits the chamber throat, the obturated bullet drags the cylinder forward, and the frame being driven backward by recoil would only serve to cause the cylinder to remain forward. (Newton 1A: An object at rest tends to remain at rest.)

Why so much concern over the B/C gap? As long as the chambers and barrel aren't badly out of alignment...unless you need maximum velocity and power, the loss of 20-30 fps is neither here nor there.

hang fire
January 19, 2012, 01:56 PM
For the most part, what you say is true, but note your theory stopped with the pressures contained within the chamber. Once the boolit leaves the chamber and enters the bore, what held true before, now needs to be revisited

Physics says for any action, there is an equal and opposite reaction. Gas is a fluid, under pressure a fluid exerts said pressure equally in all directions and seeks to occupy any unoccupied space to equalize the pressure. The hot gases pressure drives the boolit forward down the barrel, the cartridge case (which is gripping the chambers walls) and cylinder is driven to the rear, transferring resulting force to the recoil shield.

When is comes to barrel/cylinder face gap, velocity aside, there are other negatives to consider. If you were standing to one side of me when I fired a heavily soft lubed boolit, pushed by black powder gases generating several thousand pounds of pressure, through that B/C transition gap of 0.015”, one bad negative would become readily apparent to you.

1911Tuner
January 19, 2012, 03:01 PM
I understand what happens perfectly. I think the part you're failing to see is that when the gas hits the bullet base, it obturates...swells to fit the chamber throat tightly...and drags the cylinder forward in its direction of travel. The case rim is already against the recoil shield...driven by the gases and pressure. It doesn't grip the chamber wall tightly enough to drag it backward against the forward drag caused by the bullet. At the most, the two would cancel one another out

There's really nothing to drive the cylinder itself backward. So...naturally there's no damage to the shim...as you've seen.

Mac's Precision
January 19, 2012, 03:48 PM
Tuner is quite correct. There are about a gazillion K frame magnums with hammered yokes to support what he said.

I would suggest you follow what Fuff said, he is very much correct and it's wise to follow his wisdom. If you intend to fire that gun you should resolve the issues properly.

I'd suggest you clean it....oil it up good and get a cheaper modern gun and go shooting. As it sits that gun is a nice old collector piece, I'd not risk turning it into a paper weight.

1911Tuner
January 19, 2012, 03:52 PM
There are about a gazillion K frame magnums with hammered yokes to support what he said.

And stretched frames from the bullet dragging forward on the barrel while the opposite forces slam the recoil shield and frame backward. Oh, yes.

Let's try it this way. Strictly hypothetical. Maybe it'll help him understand why his shim didn't get marked.

Let's build a double-end cannnon with the chamber located precisely
in the center of the barrel.

Let's assume that the bore is perfectly round and concentric, with no
variation in diameter for the entire length. Let's also assume
a mirror finish in this bore.

Let's have two mirror finished cannonballs...also perfectly round and
precisely the same diameter. They are of identical mass.

Let's assume that the balls are a light interference fit in their bores,
so that frictional contact is present.

Let's load these projectiles precisely equidistant from their respective
muzzles, with the powder charge in the exact center.

When the gun is fired, both balls accelerate at the same rate, and both
exit their respective muzzles at the same instant, at equal, but opposite
velocities.

Which direction will the gun move?

hang fire
January 19, 2012, 04:26 PM
If that recoil shield was not there, a shooter would be wearing the cylinder in the center of his forehead.

ON C&B revolvers, the cylinder ratchet and recoil shield must soley bear the forces exerted. I have seen old well used, and possibly abused revolvers, where the cylinder ratchet was badly beat up from impact and the recoil shield was well indented with the imprint of the ratchet.

hang fire
January 19, 2012, 04:36 PM
I think the part you're failing to see is that when the gas hits the bullet base, it obturates...swells to fit the chamber throat tightly...and drags the cylinder forward in its direction of travel.

I think the part you are failing to see, is that you are repeating almost exactly what I said in my initial post.

As the bullet passes into the chamber throat, the cylinder moves forward with the bullet, stopping when the cylinder base pin bushing gas ring contacts the forward frame face.

Mac's Precision
January 19, 2012, 04:42 PM
Your talking apples and oranges there. With Cap and ball the cylinder functions AS the case. Certainly the pressure then blows the cylinder back. IN fixed cartridge design such as you were talking...the case is firmly against the standing breech and the cylinder is blown forward.

1911Tuner
January 19, 2012, 04:51 PM
I think the part you are failing to see, is that you are repeating almost exactly what I said in my initial post.

I saw that.

But...

Then you went on to say:

The pressure now forces the cylinder rapidly to the rear and the cylinder ratchet comes to bear forcefully upon the recoil shield.

And that doesn't happen. Thus the reason that your shim is undamaged.

Because, as Mac pointed out...

With Cap and ball the cylinder functions AS the case. Certainly the pressure then blows the cylinder back. IN fixed cartridge design such as you were talking...the case is firmly against the standing breech and the cylinder is blown forward.

Mac's Precision
January 19, 2012, 05:11 PM
I wish I had access to high speed photography. The amazing things that happen to all guns during the firing sequence would be a big eye opener to a lot of people. Being able to view cylinder movement, barrel whip, hammer bounce and a great many other anomalies would be a great education.

1911Tuner
January 19, 2012, 05:24 PM
Mac...Tripp Research put out a good one. It was geared more toward the 1911 pistol, but the first sequence did show an interesting bolt bounce as it went to battery in an AR15.

Mac's Precision
January 19, 2012, 05:56 PM
Yep Tuner, there is some amazing stuff that happens. I saw some footage of an AK being fired. The degree of barrel whip was AMAZING. And people wonder why they aren't tack drivers. It is amazing they can hit anything at all with the whole rifle thrashing about like it does.

http://www.youtube.com/watch?v=t1EAxSUfVk0

In that video you can see that 44 actually bounce off the shooters hands a couple times during recoil. As that gun frame recoils the cylinder would like to remain still while the frame recoils independently. What happens is the cylinder actually ends up bouncing fore and aft as do the other loaded cartridges. That said, all that happens WELL AFTER the fired bullet is long gone. The initial blast shoves the cylinder forward against the yoke and that is why it has room to get thrown back as the frame stops against the shooter's hand.

Why the shooter has TWO fingers on the trigger is unknown. Perhaps it is a technique I wasn't taught when properly firing the Dirty Harry wheel gun :D

1911Tuner
January 19, 2012, 06:02 PM
Mac, It's almost a miracle that they even stay together. I've often said that if the average man really understood how violent firing a gun is, he'd probably never pull another trigger.

1911Tuner
January 19, 2012, 06:14 PM
Anyway...back on topic.

I vote to buy a modern replica to shoot and hang that old Colt on the wall before ya break it, lad.

Mac's Precision
January 19, 2012, 06:24 PM
Sir we'd like you to put your hand next to a BIG fire....no gloves.

http://i269.photobucket.com/albums/jj61/motorcyclemac/revolverblast.jpg

Looks like a dragster launching to go down the strip.

hang fire
January 19, 2012, 08:32 PM
Anyway...back on topic.

I vote to buy a modern replica to shoot and hang that old Colt on the wall before ya break it, lad.

Hardly a lad, sonny. I have been shooting and building black powder guns for around 50 years.

http://hstrial-rchambers.homestead.com/Index.html

I guess next, I will be told to not be shooting my favorite BPCR. A JM Marlin Ballard #5 Pacific in .45-70, as mfg. around 1877-78, it is even older than the Colt.

http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P1010288.jpg

http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P1010287.jpg

hoghunting
January 20, 2012, 12:25 AM
I am not an engineer, nor stayed at a Holiday Inn last night, so any input and critique as to my approach would be appreciated.

Obviously not too appreciated as any advice they have given you has been ignored or argued. Why ask for advice if you have all the answers?

1911Tuner
January 20, 2012, 03:30 AM
Hardly a lad sonny

Sonny? I wish!

Lad...A term that I often use generically in addressing my peers. A British colloquialism...even though I'm not British.

"I've been playing darts with the lads." (Even though the lads are all well into their 60s.)

I have been shooting and building black powder guns for around 50 years.

Then you should know that some of the old (iron) ones can let go suddenly and without apparent reason...even using real black powder. (Ask me how I'd know about that.)

http://i40.photobucket.com/albums/e243/1911Tuner/McNelly.jpg

hang fire
January 20, 2012, 04:43 AM
Re: hoghuntin:

While appreciated, input and critique is not the end all written in stone, it is to be evaluated and weighed, then accepted or discarded. But, when it comes to telling me I should not be shooting the Colt, period, that was a personal opine, And when it come to such opinions, they are like a certain bodily orifice, everyone has one.

One guy did steer me to some content on shimming of the revolver recoil shield to close the B/C gap, so my idea is nothing new. On the Ruger forum even years ago, some guys were doing same as a matter of course to correct excessive B/C gap on the Ruger SA. And this was not for a low pressure black powder revolver, but for the full power magnums.

1911Tuner
January 20, 2012, 04:53 AM
On the Ruger forum even years ago, some guys were doing same as a matter of course to correct excessive B/C gap on the Ruger SA. And this was not for a low pressure black powder revolver, but for the full power magnums.

Yes. That's been done...and it's never been a problem for the shim because the cylinder isn't driven backward. It can't happen with a bored-through cylinder. It's a jerry-rig method to correct the problem, but it works.

The problem with it is that it leads many to believe that all is well when that may not be the case. If the excessive gap is the result of frame stretch, it comes with excessive headspace, and excessive headspace can result in some unpleasant surprises...even with low-pressure black powder cartridges.

But, when it comes to telling me I should not be shooting the Colt, period, that was a personal opine.

Nobody mandated anything here. Some very experienced people advised you not to...but as with anything else...the choice lies with you. Life is a crapshoot. Roll the dice.

hang fire
January 20, 2012, 05:26 AM
Re: 1911Tuner:

Just curious, I could be wrong, but why are you showing the picture of metallic cartridges with what looks to me to be an 1863 percussion Sharps replica with the Maynard tape primer system? Has it been converted to CF brass cartridge? Is it copied after one of the trial rifles Sharps submited to the US army?

About 30 years ago I converted a Sile .54 paper cartridge percussion Sharps replica to .45-70. The sweated in turned down barrel was from a Ruger #2, the breech block was of my own design.


http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P1010003-2.jpg

http://i3.photobucket.com/albums/y92/TANSTAAFL-2/P10100011.jpg

As to old guns suddenly letting go, I have no doubt that they do. Especially if they were not inspected by a competent person and were mechanically unsafe to fire as designed.

I have no idea how you would know about them failing, perhaps you could relate.

1911Tuner
January 20, 2012, 05:55 AM
Mine is a replica of an 1859 pattern "McNelly" cavalry carbine. After a few close calls with the original percussion and .50-70 conversions...I decided to take my own advice. The cool factor with an original is higher than with the Italian clones, but my eyes still see...pretty well...and my fingers are all intact. A bit stiff these days, but they're there.

Gettin' old ain't for sissies...

See...The thing is that the forum owners are responsible for what gets posted here, and we have to be on the lookout for any advice that could pose a danger to a shooter if followed.

We understand that excess B/C gap often comes with excessive headspace, but a year down the road, some guy who is obsessed with the pursuit of the nth degree of velocity may not. He sees is a quick fix for his hurdle in obtaining that last 30 fps, and that's all he sees... and he may not realize that his revolver is within .002 inch of removing his fingers. But, he thinks that his problem has been cured, and he proceeds to blast away, further stretching the frame and increasing the headspace.

But...

If he knows that the frame is stretched, he may moderate his ammunition or his usage after having the problem properly corrected by a revolver smith or an armorer.

If we post the warnings, and he blows his eyes out, he has no legal recourse...even if he didn't see them. If we don't, he can come at us with a ruinous lawsuit...and win.
But, that's not the reason for the warnings. We really don't want anybody to get hurt.

Your revolver is old, and...unless it belonged to your grandfather and your father before you...it has an unknown history. For all we know, somebody may have duplicated Elmer Keith's thunderboomer .45 Colt data before you got it and stretched the frame badly, accounting for the excessive gap.

Didn't mean for it to seem like I was beatin' on ya...but we have to post these things.

Old Fuff
January 20, 2012, 10:49 AM
But, when it comes to telling me I should not be shooting the Colt, period, that was a personal opine.

One time during a conversation with several individuals, of which I was one, Jeff Cooper (who had an international reputation for having some very strong opinions), said that everyone had a right to have one about any subject - but the value of such was dependent on the holder's experience and knowledge of the issue in question.

In the opening post you admitted to not having substantial knowledge of the technical aspects of the subject, and ask for others that might have more to submit comments. Apparently you were not happy when some of them did not endorse what you proposed to do.

On my part I do have some experience and knowledge, and the gunsmith I suggested (David Chicoine) is far and away ahead of me. If you should ask him about shooting your 1886 era Colt you would find that he not only opposed the idea, but could give you a detailed explanation as to why. His remarks might just constitute an opinion, which is true. But it would be an opinion coming from a leading authority in the field.

I didn't go as far as I think he would, because reading between the lines of your posts on this and another thread I was convinced that you were determined to continue shooting the revolver regardless of what others might say.

So I suggested that if you were going to continue shooting you could considerably reduce the risk of damage by having a modern "shooting cylinder" installed in the revolver under conditions where no modifications or changes would be made to the gun itself. Keep in mind that "considerably reduce," is not "entirely eliminate."

The chances of shooting black powder loads will not, as I have pointed out, insure that the practice won't at some point cause some damage, but it will reduce the likelihood. If you should decide to retire the six-shooter the possibility of damage from shooting would be reduced to nil. Installing a modern cylinder represents a compromise.

I am submitting this post, not because I think it will change your mind, but rather as a guide for other members and visitors who follow the forum.

hang fire
January 20, 2012, 06:39 PM
It keeps getting repeated by some that the cylinder does not get thrust to the rear in a forceful manner, yet the revolver people on the Ruger forum say otherwise.

This is what “Iowegan Retired Gunsmith” had to say on the matter, and it concurs with what I have stated.

As the bullet enters the cylinder throat, it "plugs" the hole in the throat. This causes the cylinder to thrust forward and move the same direction as the bullet. Forward movement is stopped by the internal bearing surface of the yoke/crane tube in a DA revolver or the front frame/ gas ring bearing surface in a SA revolver.

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.

http://rugerforum.net/gunsmithing/24253-revolver-recoil-physics.html

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