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

Discussion in 'Gunsmithing and Repairs' started by hang fire, Jan 18, 2012.

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  1. hang fire

    hang fire Member

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    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.


    P1010329.jpg

    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.

    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.
     
  2. Old Fuff

    Old Fuff Member

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    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.
     
  3. velocette

    velocette Member

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    Old Fuff has offered some really good advice. I respectfully suggest that you listen to his words of wisdom.

    Roger
     
  4. hang fire

    hang fire Member

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    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.
     
  5. Old Fuff

    Old Fuff Member

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    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.
     
  6. col.lemat

    col.lemat Member

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    .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.
     
  7. rbernie
    • Contributing Member

    rbernie Member

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    And, in matters such as these, that would be their loss.
     
  8. rcmodel

    rcmodel Member in memoriam

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    Well, I certainly always do.

    Sometimes!!! :D

    rc
     
  9. Old Fuff

    Old Fuff Member

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    Well now! I seem to have some support in high places... Maybe I should run for President... :D
     
  10. hang fire

    hang fire Member

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    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.
     
    Last edited: Jan 19, 2012
  11. 1911Tuner

    1911Tuner Moderator Emeritus

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    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.
     
  12. hang fire

    hang fire Member

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    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.
     
  13. 1911Tuner

    1911Tuner Moderator Emeritus

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    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.
     
  14. Mac's Precision

    Mac's Precision Member

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    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.
     
  15. 1911Tuner

    1911Tuner Moderator Emeritus

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    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?
     
  16. hang fire

    hang fire Member

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    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.
     
    Last edited: Jan 19, 2012
  17. hang fire

    hang fire Member

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

     
  18. Mac's Precision

    Mac's Precision Member

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    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.
     
  19. 1911Tuner

    1911Tuner Moderator Emeritus

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    I saw that.

    But...

    Then you went on to say:

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

    Because, as Mac pointed out...

     
  20. Mac's Precision

    Mac's Precision Member

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    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.
     
  21. 1911Tuner

    1911Tuner Moderator Emeritus

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    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.
     
  22. Mac's Precision

    Mac's Precision Member

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    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
     
  23. 1911Tuner

    1911Tuner Moderator Emeritus

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    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.
     
  24. 1911Tuner

    1911Tuner Moderator Emeritus

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    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.
     
  25. Mac's Precision

    Mac's Precision Member

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    Sir we'd like you to put your hand next to a BIG fire....no gloves.

    revolverblast.gif

    Looks like a dragster launching to go down the strip.
     
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