Adjusting cylinder gap on a Colt type BP revolver?


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ClemBert
April 19, 2011, 10:56 PM
I thought I'd start a new thread separate from my previous thread concerning the proper technique to measure cylinder gap.

This time I want to learn some new gunsmithing skills on how to adjust the cylinder-to-barrel gap on a Colt style open top BP revolver. I'm not interested in solutions that use shims nor am I interested in using the wedge as an adjustment tool.

madcratebuilder had posted the following:

The old Colt specs called for .006-.008 for the cap and ball revolvers. You can run a closer gap but risk binding if you have any powder residue build up. Colt had this problem with the Walker and changed the forcing cone shape with the Dragoon model for less surface area contact.

I've shoot these with as much as .018 gap and see little or no difference with the same model at .008.

To close the gap you have to set the barrel back, fairly easy on a open top, requires machining on a top strap model.

I posted:

On an open top what is the process to set the barrel back? Likewise, what is the process to increase the gap?

I suppose one way is the screw the barrel in or out? But, for the open tops I suppose you'd remove the barrel pins then take a little off the mating portion of the frame?

And:

If this is the process then I'd have more questions:

1. How hard is it to remove the barrel pins and do they get ruined when you remove them?
2. Wouldn't you need a wider wedge as the distance between the barrel slot and the arbor slot contact points would increase?

Y'all have really peaked my interest now as to your gunsmithing skills and how you increase or decrease the barrel/cylinder gap.

So, what say you Italian clone gunsmithers? :scrutiny:

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makos_goods
April 19, 2011, 11:50 PM
Clembert,
Read this first then we'll talk.

http://www.theopenrange.net/articles/Tuning_the_Uberti_Open_Top_Revolvers_Part_1.pdf

http://www.theopenrange.net/articles/Tuning_the_Uberti_Open_Top_Revolvers_Part_2.pdf

http://www.theopenrange.net/articles/Tuning_the_Uberti_Open_Top_Revolvers_Part_3.pdf

http://www.theopenrange.net/articles/Tuning_the_Uberti_Open_Top_Revolvers_Part_4.pdf (http://www.theopenrange.net/articles/Tuning_the_Uberti_Open_Top_Revolvers_Part_4.pdf)

I have a different way of adding a spacer to a Uberti than Pettifogger but it does the same thing. I have a bunch of illustrations on setting a few things but read Larson's articles from the Cowboy Chronicle first.

Regards,
Mako

Cop Bob
April 20, 2011, 04:01 PM
Great info in the links, thanks for that post... makes me really glad I hae a Mill and a Lathe..
A bit tricky for the average do it yourselfer, but patience is the key

Be sure that the directions are followed Exactly ... #3 locator button, whoda thunk!

ClemBert
April 21, 2011, 04:07 PM
Mako,

Thanks for posting those links. Very useful info there. Unfortunately, his tune up procedure doesn't answer the question I had regarding reducing the cylinder gap on an open top revolver. Mr. madcratebuilder indicated he had an easy solution but has yet to chime in.

I'm picturing that the process is to remove some material off of the frame. That area that mates to the barrel. I would suppose you'd remove the barrel pins, possibly ruining them, then file off whatever amount you needed to close the gap. However, that would mean you'd need a wider wedge to account for the increase in the delta between the two contact points in the arbor/barrel window.

I have a brand new unfired 1860 with a 0.0125 gap that could be the perfect project gun. I should have been smart enough to measure the cylinder gap when I first opened the box then rejected it accordingly. But that change was a year ago. :banghead:

junkman_01
April 21, 2011, 06:09 PM
You take material off the barrel lug, not the frame.

denster
April 21, 2011, 06:28 PM
Junkman is correct. Remove material from the barrel lug. Best done on a mill unless you are very good with a file. The small amount you are removing you should be OK with wedge fit it wil just go in a little further. If you have a Pietta you will need to remove the same amount from the end of the arbor.

ClemBert
April 21, 2011, 06:36 PM
What's the thinking behind taking it off the barrel side? Because it's easier to buy a barrel if you screw up? It is a Pietta.

What do you do to deal with needing a larger wedge?

denster
April 21, 2011, 07:37 PM
"quote" What's the thinking behind taking it off the barrel side? Because it's easier to buy a barrel if you screw up? It is a Pietta.

What do you do to deal with needing a larger wedge?

That is one consideration. Also the frame is case hardened the barrel is not and it is easier to clamp the barrel in a mill or vise. There are other considerations but I don't want to write a book.
Need a larger wedge? Make one it's not hard.

ClemBert
April 21, 2011, 08:26 PM
What would you do if it was an 1851 design. Would cutting the barrel side basically mean you would be cutting a groove or notch? I would think it would make it look funny.

Is the case hardened steel that hard to file? I see in the tune up procedures they are often drilling holes into the case hardened steel to install a plunger/spring to replace the spring on the hand.

junkman_01
April 21, 2011, 08:29 PM
What would you do if it was an 1851 design. Would cutting the barrel side basically mean you would be cutting a groove or notch?
I've seen that done too.

makos_goods
April 21, 2011, 09:54 PM
Clembert,
Don't get too excited yet. I'm going to put something together for you. But, you missed the point of Pettifoggers articles. If you are going to this much trouble then you need to do it right and set your arbor length first. Once that is set then you will proceed to set your gap. And Junkman is right there are even original Colt's '51s with a slight step in them when they set the gap.
~Mako

ClemBert
April 21, 2011, 11:11 PM
In this thread started by madcratebuilder (http://www.thehighroad.org/showthread.php?t=531877&) it would appear that he takes some off the frame. I wonder how he gets those pins out.

Mako, I'm going to have to remove some material from the 1860's arbor since it's a Pietta and the arbor bottoms out.

denster
April 21, 2011, 11:43 PM
If your arbor bottoms out in the hole at the same point that the barrel lug meets the frame and the B/C gap is still too large then you will have to remove metal from the barrel lug and the same amount from the end of the arbor.
To answer your questions. Yes the case hardened frame is hard generally a file will just slide over it. As to drilling the holes a high speed steel or cobalt bit will generally cut through, I prefer using a carbide bit as it takes the maybe out of it. As to removing metal from the lug as opposed to the frame. It's just a lot easier to get it right. On an 1851 you carry the removal up to the loading cut out that way whatever line there is only shows on the left side and you would really have to look to see it. Remember you're only taking off .004 to .006 of an inch.

makos_goods
April 22, 2011, 12:27 AM
In this thread started by madcratebuilder (http://www.thehighroad.org/showthread.php?t=531877&) it would appear that he takes some off the frame. I wonder how he gets those pins out.

Mako, I'm going to have to remove some material from the 1860's arbor since it's a Pietta and the arbor bottoms out.
Excellent! For some reason I was thinking it was a Uberti. This makes the fitting easier because we don't have to add a spacer.

I'll adjust accordingly.
~Mako

J-Bar
April 22, 2011, 03:06 PM
I believe the cylinder gap changes from uncocked to cocked condition, does it not?

Forward pressure from the hand pushing on the back of the cylinder moves the cylinder forward during cocking, and the bolt then locks the cylinder in the more forward position, where it remains until the hammer is dropped and the bolt released. I think...

So wouldn't one have to take that phenomonon into account when considering cylinder gap?

Or am I full of it? (wouldn't be the first time)

ClemBert
April 22, 2011, 03:10 PM
Well J-Bar, you could test your theory and get back to us. Measure your cylinder gap with hammer down, hammer half-cocked, then hammer at full-cock. In all instances push the cylinder back rearward as far as you can while inserting the feeler gauge. Interested in seeing your findings.

ClemBert
April 22, 2011, 03:12 PM
Excellent! For some reason I was thinking it was a Uberti. This makes the fitting easier because we don't have to add a spacer.

I'll adjust accordingly.

The only open top Uberti I have is a Walker. I use two thin washers sitting on top of the arbor of that revolver to fix that problem.

J-Bar
April 22, 2011, 03:30 PM
Well J-Bar, you could test your theory and get back to us. Measure your cylinder gap with hammer down, hammer half-cocked, then hammer at full-cock. In all instances push the cylinder back rearward as far as you can while inserting the feeler gauge. Interested in seeing your findings.
I will!

I am about 150 miles and three hours away from being able to do that at the moment, so others may want to confirm or refute the idea in the meantime...

J-Bar
April 22, 2011, 08:25 PM
OK, I am maybe 90 % full of it, not quite completely!!

First off, please understand I am not a machinist or a gunsmith, just a cowboy action shooter who is trying to learn more about how these things work. I enjoy reading your posts as well as others; I am not trying to convince anyone of anything, so please have patience with stupid questions.

Grovel mode off.

Following Clembert's instructions on measuring the gap, pushing the cylinder to the rear throughout the cycle, the gap will of course stay the same. But when I am shooting in a match, there is nothing to push the cylinder backwards while I am cocking the hammer. I can hold the gun up to a bright light and watch the barrel-cylinder gap close all the way while slowly cocking the gun. Pressure from the hand does push the cylinder forward, and as best I can tell the cylinder appears to be in contact with the barrel at full cock. A feeler gauge leaf can be pulled between the cylinder and barrel, but it appears that the hand is holding the cylinder against the barrel at full cock.

Now when the trigger is pulled, the hand retracts back into the frame, and the force of the ignited gasses pushes the cylinder to the rear and re-establishes the true fixed gap opening. We can tell that the gap re-opens from the smoke and crud that comes out between the cylinder and barrel when the gun is fired.

As a competitor using these in a match, it's aggravating to have a particular gun start to become hard to cock during a stage, and I think this temporary narrowing of the gap during cocking plays a part. I have 4 different Uberti 1851 London Navies (steel frame). Two are disassembled at the moment for cleaning after a match. I measured the gaps on the other two, and was surprised to find one is .006 and the other is .019. I like the .019...it never binds up during a match. For my purposes, .006 is too narrow.
Both of these revolvers have had the Pettifogger fix; the arbors are fitted nicely.

I will post a separate thread if you think I am taking this one off topic. But I would appreciate suggestions on the best way to open the gap several thousandths. Would dressing the barrel face with file or abrasives create other problems?

Thanks for your patience and ideas.

Smokin'Joe
April 23, 2011, 06:34 PM
I reduced the barrel to cylinder gap on my brass frame Pietta from .008" to .004". First I removed the alignment pins with Vise Grip pliers. They pull straight out. They were slightly dented in the process but they are soft steel and were filed smooth and reused.

http://i1215.photobucket.com/albums/cc510/SmmokingJoe/IMG_00051.jpg?t=1303593931

Insert arbor into recess in barrel and twist barrel and frame side to side while holding abrasive paper or cloth between the two. This technique will allow you to remove metal from either or both surfaces. A like amount of metal was removed from the arbor to allow for proper mating of the two parts.

http://i1215.photobucket.com/albums/cc510/SmmokingJoe/IMG_00151.jpg?t=1303593852

On my gun the wedge is still quite usable. It seats in deeper but still does its job. I did, however, notice that the clearance between the wedge spring rivet and the wedge retaining screw was pretty close so I filed the screw head down to increase the clearance at that point. Reinstall the alignment pins with Lock Tite if you feel the need.

Norton Commando
April 23, 2011, 07:16 PM
Hey Smokin Joe,

Great technique and photographs; thanks!

Jason

ClemBert
April 24, 2011, 11:53 AM
Great job Smokin'Joe!

Looks like you are the only one brave enough to remove those barrel pins so far. Thanks for the report. :) I like the idea of taking the material off of the frame like you did. There's probably no evidence that the gap job was ever done. If that is a Pietta I'm surprised you didn't have to take a bit off the end of the arbor.

CharlesK80
April 24, 2011, 11:17 PM
This is a great thread. Am waiting for Makos input who was going to put something together.

As a side note, I too used, yesterday, washers in my A.Uberti ’51 Navy (Western Arms) to get the arbor length correct. Gap, with cylinder pushed full back and hammer cocked is .008” to .009” depending on the chamber. And is repeatable. Previously, was not.

I must say that all of my (3) BP revolvers had rough, sticking arbors which gave variable gaps until both the end and shaft of the arbor were polished to remove the rough surface. All are ASM and A.Uberti clones. All required washer(s).

After polishing, the arbor now enters and bottoms the hole with a smooth and satisfying “click” on each gun.

makos_goods
April 26, 2011, 03:46 PM
WARNING: Any modification to a firearm can be dangerous. If you are unsure of anything in this or any other posting seek the help of a qualified gunsmith before attempting any changes.


Setting the Cylinder Gap on any Colt’s pattern percussion pistol is basically done in the same manner regardless of the manufacturer, the primary difference being whether or not a spacer has to be added to the end of the arbor as is necessary with the Uberti pistols.

Follow with me because it sounds complicated but it’s easily accomplished if we are careful and understand a few things.

In a perfectly fit and assembled pistol the arbor will bottom out in the hole of the barrel lug, while at the same time the barrel lug will be fully flush with the frame. This is held together by the wedge which pushes the barrel back against the arbor face and the frame front face by engaging the wedge taper against the front edge of the arbor slot and the rear edges of the barrel slot. All of this takes place with the wedge being inserted to a consistent depth and the cylinder gap being .008”-.010”.

This “could” be a tall order because several things have to be fit almost exactly for all of this to come about. But it can be accomplished and even the confusing statement above can be fully understood and explained to others.

In the 19th century Colt’s individually fit each pistol before it left the factory and the cylinder gap was set with the arbor. Even a very worn original Colt’s pistol will usually have a decent cylinder gap running between .006” and .012” which is testimony to the fitting and the design. The exception to this will be when the arbor has become loose in the threads where it attaches to the frame. If it wobbles a bit the gap will usually be affected. Sometimes the wobble isn’t apparent until the barrel is removed because the multiple contact lock-up stabilizes the barrel.

The original design intent after evaluating the Colt’s design is not what some have written about or has become “common wisdom” among percussion pistol shooters in the 20th and 21st centuries. The Wedge is not primarily an “ADJUSTMENT” device. It is a LOCKING device which was commonly used in firearms in the 17th through 19th century firearms. One can look at many flintlock and percussion rifles with the mortise and tenon joints holding the barrels in location and the wedges (tenons) sometimes with retaining springs just like the Colt’s pistols to understand how they were used and to what primary purpose the taper on the wedge served. It is true the taper will allow a worn component to continue to fit longer than a straight sided part, but the primary purpose of the taper was to lock (“wedge”) the piece in place.

It is obvious pistols will work to some degree without this perfect balance of dimensions and two extremes of fit can be seen looking just at the Uberti and the Pietta pistols. Pietta pistols have arbor fits that are usually closer to being ideal. (Don't assume from this I prefer Pietta Colt's reproductions, I actually find the Uberti pistols to be more authentic and better made, the arbor is the only exception.)

Uberti Pistols have arbors which are always too short from the factory. Uberti accomplishes their cylinder gap by making use of the taper on the wedge to open or close the gap. The problem with this approach is that it isn’t as repeatable in the field and isn’t as stable as a correctly fit pistol. This method has also led to some of the misconception modern shooters have about the correct method of setting the cylinder gap and what it should actually be set to.

Because Pietta attempts to mass produce an arbor to the correct length with minimal factory fitting we sometimes see an arbor which is too long and a cylinder gap which cannot be closed to the ideal maximum opening of .010”. The barrel will bottom out on the arbor and no amount of force from the wedge will close the gap. On these pistols it is common to see a small gap where the barrel lug meets the frame once again because the barrel is bottoming out prematurely on the arbor.

Fortunately there is a better way to assure intimate contact with all four surfaces ( arbor, arbor hole, barrel lug and frame front face) using the natural elasticity of the steel to accomplish not only an intimate contact, but a spring locked fit as well. This fit will last for many years, it may relieve itself of the elastic “interference,” but it will then settle into an intimate surface to surface fit that won’t change unless damaged.

We will first deal with pistols such as the Piettas and others including the originals that have arbors of correct or near correct length.

First we will set the dimensions so the barrel lug contacts the frame leaving a .010”-.012” gap at the cylinder. Then upon insertion of the wedge the barrel will be pulled down into hard contact with the end of the arbor which had a .001”-.002” gap before the wedge insertion. The cylinder gap will close to .008”-.010” which is the ideal gap. The assembly will be very tight and the wedge will not move because the barrel is slightly sprung to close the end of the arbor gap.

To measure and modify the pistol first fully strip it down to the Frame, Cylinder and Barrel. For most of the measurements a wedge is not needed and the “wedging action” is definitely not desired. PLEASE NOTE, a wedge can be used only if it is carefully partially inserted to keep the components in place, but extreme care must be taken not to insert the wedge beyond initial contact with the front of the Arbor slot and the rear of the barrel slot. In other words don’t let the tapered wedge act as a “spreader” and move the barrel back.

First place the cylinder on the frame and insert the barrel as show in Fig. 1

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig1.png

Use a feeler gage to determine the gap. Without the internal components the cylinder will fully move to the rear. Assure that the lug is fully butted against the frame for this measurement. You may wish to insert the wedge into the slot just enough to take up any slack but do not insert it any deeper than necessary, do not let the taper on the wedge push the barrel back. If you can’t easily pull the wedge out with your fingers it is in too deep.

If you use a wedge you should double check your measurements with the wedge removed. To do that hold the pistol with the barrel pointed up then insert the gage, it should fit, but not lift the barrel away from the frame.

Record this measurement, ideally it will be .009”-.012”. It will close down once we insert the wedge (this will be explained later).

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig2.png

Now measure the gap with the barrel rotated as shown in Fig. 2 and Fig 3, keep the barrel lug from engaging the frame.

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig3.png

The barrel must be bottomed out on the arbor for this measurement to be accurate. If there isn’t any gap then see the explanation in the post about the Uberti pistols to create a spacer. Record this dimension. Ideally it will be .008”-.010”, which will be our final gap at assembly.

Record this dimension, keep in mind when finished it needs to always be .001”-.002” smaller than the first dimension recorded. If it is larger than the dimension recorded in Fig. 1 then we know the barrel will balance on the end of the arbor and not correctly contact the frame at the lug face.

If the dimension in Fig. 3 is greater than .010” then we will adjust it by removing material from the arbor as shown in Fig. 4.

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig4.png

Removal will be a one to one relationship. If the gap measures in Fig. 3 was .013” then removing .004” from the end face will close the gap to .009”. The arbor can be shortened with either a file or machined in a mill. Keep the end square and perpendicular to the axis of the arbor.

If the gap measured in Fig. 3 was less than .008” but only by a few thousands of an inch (I wouldn’t hesitate doing this if it were .005” or less) the gap can be increased by removing material from the barrel face at the forcing cone as shown in Fig. 5.
http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig5.png


Once you have determined the gap now measures .008”-.010” when measured as shown in Fig. 3 put the barrel back on as shown in Fig. 6 and re-measure.


http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig6.png

We will now adjust the barrel lug to make this dimension .009”-.011”. It is important to remember this dimension needs to be .001”-.002” greater than your new dimension just measured above.

If the dimension is greater than the .001”-.002” difference you are looking for then remove material from the lug as shown in Fig. 7. You may use a file or a milling machine.

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig7.png

In the case of a barrel that doesn’t have a through full clearance like the ’60, ’61 and ’62 Police models a step can be machined in the lug as shown in Fig. 8.

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig8.png

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig9.png




If it is carefully cut it won’t even be apparent when it butts up to the frame. As shown in Fig 9.

Your fits should now be as shown in Fig. 10.


http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig10.png


Personally I like the wedge to fit as shown in Fig. 11

http://i627.photobucket.com/albums/tt358/Mako_CAS/Fitting/Fig11.png

Where the hook on the wedge spring just clears the barrel as it exits slot. This allows an easy visual reference for the correct insertion and in the event of wear will allow the wedge to be inserted deeper to take up any difference. If the wedge is deeper it will work fine, this is just my preference for a fresh pistol at initial set-up.

In a future post I will show a bit different spacer for the Uberti frames. The Uberti frames are set in a manner just like the instructions above, the only difference is that there must be a spacer added to the end of the arbor before you set the gap. Failure to add a spacer puts you at the mercy of the wedge taper

~Mako

junkman_01
April 26, 2011, 04:59 PM
Mako,

That is a great tutorial. I'm saving it in my notes. I'm waiting with bated breath for the Uberti installment.

ClemBert
April 26, 2011, 05:01 PM
Mako,

The precision, attention to detail, and faithful reproduction of the open top revolver in your 3D drawings is ridiculously AWESOME! All the way down to the port in the nipples...WOW! I have a man crush on your artistry and CAD skills! :D

Thanks for taking the time to give the specific details on how to close the gap on an open top revolver. I think your drawings with instructions should be put in their own thread and kept on top as a sticky thread.

denster
April 26, 2011, 10:19 PM
Makos. My hats off to you that was well done.

Norton Commando
April 27, 2011, 10:27 AM
Beautiful illustration indeed!

Jason

Smokin'Joe
April 27, 2011, 01:33 PM
Personally I like the wedge to fit as shown in Fig. 11


MG, How do you get the wedge to fit like you want it to after all of your modifications? Do you also modify the wedge?

Norton Commando
April 27, 2011, 02:04 PM
makos_goods,

I'm surprised that the lug compresses 0.001"-0.002". Wouldn't you need something on the order of 43,500 psi to get that much compression?

Also, someone should probably make this excellent procedure and drawings a "sticky"

Jason

makos_goods
April 27, 2011, 02:49 PM
MG, How do you get the wedge to fit like you want it to after all of your modifications? Do you also modify the wedge?
Joe,
With a new or unworn pistol you will probably find that the original Wedge works fine with out any work. In the case of Clembert who needs to close the gap on his Pietta .004"-.005" he might want to buy a new wedge. They are always a bit wide. I end up working the sides of them on 400 working to 800 grit wet and dry paper slowly working the size down to get the fit.

With Uberti Wedges I find the gap from the factory is usually a bit tight and they have plenty of meat on them they usually need to be worked down once the arbor length is set.

I have two fresh Uberti wedges I have in my parts bin, but I've only ever used one and it wasn't for my pistol. I keep those and any part that could get lost on hand. I have the wedge that was replaced in my shooting box in the case I lost a wedge at a match. It was abused with a steel hammer so it's not pretty anymore, but it will fit in a pinch.

I only have one pair of Pietta Colt's pattern pistols and I haven't done much with them other than shoot them a couple of times, but the gaps are within the range to be fixed as I described, I would expect to be able to use the wedges that are in them.

If you needed to widen the wedge it could be upset with a hammer or in a press and then cleaned up. I know a few people make their own, and there is a place in Britain you can buy oversize wedges. Actually they have reproductions of original Colt's parts as well .

~Mako

makos_goods
April 27, 2011, 02:59 PM
makos_goods,

I'm surprised that the lug compresses 0.001"-0.002". Wouldn't you need something on the order of 43,500 psi to get that much compression?

Also, someone should probably make this excellent procedure and drawings a "sticky"

Jason

Jason,
That would be hard...

Look at where the force is. It's not inline with the lug, it is off to the side. It's not a direct side load, but you could calculate the vector if you wanted to go to the trouble. In the case of a '60 or '61 it's the lug "extension" that gets deflected. DEFINITELY not compressed. I'm sure some of it is taken up with biasing the components such as the arbor in the hole, etc.

If you can compress steel using a wedge on a Colt's pattern pistol I'm going to start saying "sir" to you in my responses. :D

Regards,
Mako

A. Walker
May 1, 2011, 01:12 PM
Personally, I think this thread should be a stickie...

Great info and excellent modeling to boot. Thanks!

Norton Commando
May 1, 2011, 01:45 PM
Personally, I think this thread should be a stickie...

I agree!

Great information and illustrations by Makos and clever technique by Smokin'Joe for removing material from the barrel and or frame while keeping surfaces parallel!

Jason

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