Barrel to Cylinder Clearance

[JoeMich]

I have a new Uberti Colt 1862 Pocket Police, and I can not see any clearence between the rear end of the barrel and the front of the cylinder. My other revolvers show a very tiny amount of light between these two surfaces. In fact, when putting the barrel onto the frame, I have to force the barrel back hard in order to start the wedge into place. I understand that there should be .004” to .006” clearance between the barrel and cylinder.How do I go about adjusting this clearance?

 

[TrapperDude]

My revolver is a Remington, so I don't have an open-top model from which to convey actual experience. However, I've heard of this problem and read some explanations for your problem, and they all seem to indicate a short arbor being the issue.

The common easy fix I have read is to find a washer of the right thickness to use as a shim to add length to the end of your arbor. That will set your barrel a touch farther forward, opening that cylinder gap in the process.

Research fixing a short arbor to get more detailed explanations. The writers of those posts will give you a better explanation of the process than I can.

 

[44Bro]

Start by fixing the arbor, as said. Then if you cannot start the wedge, mark the lower lug of the barrel where it hits the frame and start filing the barrel lug. Check the fit often!!!! The best gap setting is actually around .0015-.0025" Less fouling goes sideways, more energy goes downrange. This procedure is how Colt did the fitting in the 1850's. Look closely at pics of older guns and you can see what I'm talking about. After getting the arbor and barrel gap correct, then fit the wedge, you may need to file the wedge on the flat edge. Again check the fit often!!

 

[golden sky]

can you post a picture of your fire-arm?

my revolver requires me to unscrew the barrel, so one would screw barrel into receiver, check gap with shimstock. if too tight i would have to chuck into a lathe and remove some shoulder material from the barrel, until it's with in spec

 

[Erwan]

The problem with the Uberti is that they never have the shaft in the bottom, which creates some small inconveniences...
You can adjust it with a screw in the axis of the cylinder or with a screw or a washer fine adjusted at the end of the shaft...
A screw in the axis and a small blow of file to adjust, and that works well...
What I did :

 

[45D]

The most misunderstood thing about the open top design is the importance of the arbor length. It is the arbor that defines the barrel/cylinder clearance ("endshake" for the modern term). With the wedge "driven in" as per Colt's instructions, tension is set and the harmonics of the assemblage is as with a single unit. Basically that means the revolver won't beat itself up and you will have the same revolver each time it's assembled rather than something "close". (The wedge screw is a wedge retainer and not an adjustment device)
I use a single S.S. spacer mounted in the barrel assy for the arbor end to contact. I don't like a screw of any kind in the end of the arbor for this fix as it is of a smaller diameter (since it is threaded into the arbor) and a poor substitute for the arbor itself. Some build up the end of the arbor with Weld and dress it down appropriately.
I use a bbl/cyl clearance of .0025" - .003" ( .0015" - .002" for unmentionables).

So far, every reproduction from every manufacturer I've had in the shop has had a short arbor save for the Piettas of the last dozen or so years.

Mike

 

[JoeMich]

Gentlemen, you all diagnose my problem being arbor length, which is a common Pieta fault. The solution suggested is to use a shim to “make the arbor longer”. Simple solution. My sincere thanks for your input!!

 

[Phil Coffins]

Here’s how my Uberti shoots after I fixed the arbor and set the gap to .002”, there are five shots in this group.
IMG_0453 by Oliver Sudden, on Flickr

 

[45D]

Very nice sir!!

Mike

 

[Brokenbear]

45D's pinky finger knows more about this subject than i totally know so know the following is a questionfor my own knowledge
When the wedge is installed though while new hard to start..does the cylinder drag when you cock it?
If not ..does not the wedge area have normal wear from use that will loosen allowing easier insertion of the wedge which in turn will naturally open the cylinder/forcing cone gap (end play)?

Bear

 

[45D]

Until the arbor length is addressed you can always have the cylinder drag against the barrel so . . . The wedge will wear some over time but should always be driven in (to impart tension) and likewise out. So it should never be a "finger tight" situation. You can't get the same tension with "finger tight".
The reason it is a clearance or endshake is because there is no bushing to create a defined opening which is . . . a gap.
What's nice about this setup is that it DOES allow contact (each time it's cycled) which makes it " self cleaning "(!) so with the oldest Colt design you can get away with such a small amount of endshake! Keeps the revolver much cleaner as well!!

Mike

 

[44Bro]

So I found the pic I downloaded, don't remember where I got it from. It clearly shows how the originals barrel to frame joints were fitted.

 

[M. De Land]

I have a new Uberti Colt 1862 Pocket Police, and I can not see any clearence between the rear end of the barrel and the front of the cylinder. My other revolvers show a very tiny amount of light between these two surfaces. In fact, when putting the barrel onto the frame, I have to force the barrel back hard in order to start the wedge into place. I understand that there should be .004” to .006” clearance between the barrel and cylinder.How do I go about adjusting this clearance?

You will probably be able to push the cylinder back against the recoil shield after assembly and make a gap. The ratchet spring pushes the cylinder ahead via the ratchet/pawl toward the barrel when the revolver is assembled. If the revolver will cycle without hanging up while clean then leave it alone, it will open up with use.
The good thing about open top revolvers is that one can adjust the point of impact both in elevation and windage from frame, barrel slots and wedge manipulation. Wedge and arbor fit are only two of the adjustment points. There are two more , barrel slots on either side of the arbor and lower barrel lug length and square.
Most open frame guns will show more gap at the top of the barrel cylinder interface and will be tighter to one side while at battery. The idea , in my opinion is the top of the gap should be tighter when the gun is at battery and the sides equal so when the ball hits the forcing cone of the barrel at ignition the gap will be square around the perimeter as the pressure moves the barrel forward and away from the cylinder and frame.
One more point, I've never seen the need for the end of the arbor to bottom out in the arbor well as all the pressure at firing is in the opposite direction .
It is a convenient method of key depth index but serves very little purpose other wise. Open frame guns were designed to flex just like a bridge, trying to make a flexing design solid by loading the arbor end does not add one bit to the revolvers accuracy.
Having all pressure points and gaps plum and square when the ball hit the barrel does produce accuracy.

 

[45D]

You will probably be able to push the cylinder back against the recoil shield after assembly and make a gap. The ratchet spring pushes the cylinder ahead via the ratchet/pawl toward the barrel when the revolver is assembled. If the revolver will cycle without hanging up while clean then leave it alone, it will open up with use.
The good thing about open top revolvers is that one can adjust the point of impact both in elevation and windage from frame, barrel slots and wedge manipulation. Wedge and arbor fit are only two of the adjustment points. There are two more , barrel slots on either side of the arbor and lower barrel lug length and square.
Most open frame guns will show more gap at the top of the barrel cylinder interface and will be tighter to one side while at battery. The idea , in my opinion is the top of the gap should be tighter when the gun is at battery and the sides equal so when the ball hits the forcing cone of the barrel at ignition the gap will be square around the perimeter as the pressure moves the barrel forward and away from the cylinder and frame.
One more point, I've never seen the need for the end of the arbor to bottom out in the arbor well as all the pressure at firing is in the opposite direction .
It is a convenient method of key depth index but serves very little purpose other wise. Open frame guns were designed to flex just like a bridge, trying to make a flexing design solid by loading the arbor end does not add one bit to the revolvers accuracy.
Having all pressure points and gaps plum and square when the ball hit the barrel does produce accuracy.

So it's just a fluke that the originals did but no reproductions don't? Engineers in the mechanical age understood harmonics (they weren't nearly as stupid as some would have you believe . . . WE are the dumbed down ones!!! ) and harmonics will destroy mechanical devices. The whole reason for the arbor to bottom out under tension is to allow transmission of waves of force (harmonics) so the two assemblies would work as one instead of fighting against each other. Balance is everything in mechanics.
I was pretty much raised in a garage repairing cars, building engines, carbs, . . . anybody that has any inkling of mechanical engineering knows this. Vibration will destroy any mechanical device . . . typically in short order, definitely over time. So, this being a public forum I'll just say I disagree with most everything you posted even though it is your opinion.
There is no way that tapping a wedge in just so (not under tension) would be repeatable each time the revolver was assembled. In fact, if the wedge is allowed to just be there, it can in fact be in a different position from shot to shot. I personally have had wedges deform so badly that I could hardly remove the wedge when cleaning.
Why do you think Colt's own instructions would have you"drive the wedge in . . . "? To lock it up?

Mike

 

[M. De Land]

So it's just a fluke that the originals did but no reproductions don't? Engineers in the mechanical age understood harmonics (they weren't nearly as stupid as some would have you believe . . . WE are the dumbed down ones!!! ) and harmonics will destroy mechanical devices. The whole reason for the arbor to bottom out under tension is to allow transmission of waves of force (harmonics) so the two assemblies would work as one instead of fighting against each other. Balance is everything in mechanics.
I was pretty much raised in a garage repairing cars, building engines, carbs, . . . anybody that has any inkling of mechanical engineering knows this. Vibration will destroy any mechanical device . . . typically in short order, definitely over time. So, this being a public forum I'll just say I disagree with most everything you posted even though it is your opinion.
There is no way that tapping a wedge in just so (not under tension) would be repeatable each time the revolver was assembled. In fact, if the wedge is allowed to just be there, it can in fact be in a different position from shot to shot. I personally have had wedges deform so badly that I could hardly remove the wedge when cleaning.
Why do you think Colt's own instructions would have you"drive the wedge in . . . "? To lock it up?

Mike

Have you tested or even talked to any one who has shot and comparred accuracy with bottomed out arbors and not ? If you had you would know better !
A much more consistent method of setting your wedge depth is to make a steel gauge to go under the wedge head ledge when tapping it in or making a new one and setting the ledge thickness to accomplish the same.

 

[TrapperDude]

@M. De Land and @45D :

As a soon-to-be owner of an open-top revolver, I am enjoying your discussion about arbor and barrel mounting. What I've gathered from your discussion is that the base of the barrel trunnion(?) should be flush with the bottom of the frame and plumb for 360 degrees to ensure no vibrations which would cause harmonic effects off-center, correct?

As for the arbor itself, the best situation would be to have the length such that the trunnion to frame contact will be flush at a point where the cylinder gap is also ideal, correct?

Wouldn't varying the amount of insertion for a barrel wedge only apply if the arbor were short? It seems that in theory, an arbor that's exactly the right length would yield no response from varying wedge insertion distance except to allow the barrel to move back and forth because of the space still remaining between the wedge and the slot in the arbor on both sides of the wedge. If the arbor were too short, on the other hand, inserting the wedge would result in its movement of the barrel farther to the rear as the wedge were inserted farther. Understanding that, it makes sense that one could shave down the forward (muzzle end) edge of the wedge to cause only a certain amount of rearward movement of the barrel until it reached its ideal position.

If the arbor were too short, however, wouldn't the trunnion(?) also be too short, given that the machinist would have sized it to ensure a flush fit when the barrel assembly was installed onto the arbor? If that part were too short, how would you then correct the issue?

 

[45D]

Have you tested or even talked to any one who has shot and comparred accuracy with bottomed out arbors and not ? If you had you would know better !
A much more consistent method of setting your wedge depth is to make a steel gauge to go under the wedge head ledge when tapping it in or making a new one and setting the ledge thickness to accomplish the same.

Sir, that's why I do what I do!! If it made no difference I wouldn't go to the trouble of correcting the arbor length!! I almost find it amazing that someone on a forum today hasn't ever (apparently) heard of this !?
You obviously don't have a clue about the forces produced when the revolver is fired and how a wedge would stay in place just because you want it to. I'm sorry, I can't help you.

When I go to the range my Dragoons have a clearance of .002" . After I shoot 50 to 100 rounds of 45C at roughly 1000 fps my Dragoons still have a .002" clearance. They are as solid as a single unit frame. Before, when I shot a lot of bp the Walkers, Dragoons, Armys and Navys all would eventually shoot loose. The wedges would bend, the slots would have material moved . . all signs of an ill fitting wedge.
Since I've been correcting the arbors, there is absolutely none of the problems, the revolvers have a different feel (more like a solid revolver) and I have the same revolver after assembly and I don't have to check it with a gauge.

Trapperdude, you are correct. The only way the wedge can vary the amount of endshake you want at any given time would mean the arbor couldn't prevent the movement of the barrel assy. . . in other words, it would have to be short. By the same token, the only way to have the same revolver each time you assemble it is to have the arbor be the structure that determines how far the barrel assy can be installed . . . which is exactly what it does.
The correct or accepted parlance for what you are calling the "trunnion" is the barrel "lug". It is the lug that has the two holes that receive the locating pins mounted in the frame. Your thinking is right on though!

Mike

 

[TrapperDude]

Trapperdude, you are correct. The only way the wedge can vary the amount of endshake you want at any given time would mean the arbor couldn't prevent the movement of the barrel assy. . . in other words, it would have to be short. By the same token, the only way to have the same revolver each time you assemble it is to have the arbor be the structure that determines how far the barrel assy can be installed . . . which is exactly what it does.
The correct or accepted parlance for what you are calling the "trunnion" is the barrel "lug". It is the lug that has the two holes that receive the locating pins mounted in the frame. Your thinking is right on though!

Mike

Thanks for the great information, 45D. My current (and first) revolver is a Remington NMA. I was previously confused the first time I heard the terms "arbor" and "wedge" because my Remington has neither. I figured out what a wedge was when I got my flintlock Traditions Trapper, though.

I'm hoping that new Pietta 1860 Army shows up ready for prime time, but if it needs a little surgery, at least I won't be in the dark after reading this.

 

[jefair1]

The most misunderstood thing about the open top design is the importance of the arbor length. It is the arbor that defines the barrel/cylinder clearance ("endshake" for the modern term). With the wedge "driven in" as per Colt's instructions, tension is set and the harmonics of the assemblage is as with a single unit. Basically that means the revolver won't beat itself up and you will have the same revolver each time it's assembled rather than something "close". (The wedge screw is a wedge retainer and not an adjustment device)
I use a single S.S. spacer mounted in the barrel assy for the arbor end to contact. I don't like a screw of any kind in the end of the arbor for this fix as it is of a smaller diameter (since it is threaded into the arbor) and a poor substitute for the arbor itself. Some build up the end of the arbor with Weld and dress it down appropriately.
I use a bbl/cyl clearance of .0025" - .003" ( .0015" - .002" for unmentionables).

So far, every reproduction from every manufacturer I've had in the shop has had a short arbor save for the Piettas of the last dozen or so years.

Mike

How about putting a bolt with a karger head, filing the head until it is the same diameter as the arbor then adjusting depth?

 

[M. De Land]

Barrel harmonics are not an issue in the short length of revolver barrels however frame, slots (all three of them) wedge shape and lower lug fit do effect point of impact, accuracy and longevity. The arbor doesn't care if it hits bottom or not because all the force at firing is forward away from end load tension of the arbor, if it exists . Loading the end of the arbor in it's well has no appreciable effect on accuracy or longevity and it seems at least Pietta has figure this out!
A gun with proper fit of the mentioned load points will shoot every bit as accurately and as long without any more wear as one will with the arbor bottomed out.