Appropriate cylinder gap for Colt revolvers

[Dude]

Contact at the frame and lug has to come first. Then you adjust for endshake.

Mike

Unless the arbor is too long, the frame and cylinder lug will always meet. Does that, or has that, ever happened? So I don't follow you.

How would you adjust excessive endshake without bringing the barrel and frame closer together?

 

[45D]

Unless the arbor is too long, the frame and cylinder lug will always meet. Does that, or has that, ever happened? So I don't follow you.

How would you adjust excessive endshake without bringing the barrel and frame closer together?

You DO bring them together . . . first . . . and THEN ( dress your spacer) find your endshake number.

That way, when the wedge is driven in, there will be Hugh tension imparted at the frame/ lug ( cause they meet first). The two assemblies will be under great tension . . . which is what you want.

Mike

 

[Dude]

Let's see if I'm tracking with you:

**** the barrel to the side so the frame and barrel lug don't mate up.

Set up the arbor (adding or subtracting length as required) so it bottoms out at the correct endshake.

Now here's where I think differently.

You're saying the frame and cylinder lug will meet first, then the wedge pulls the cylinder back farther. How much of an offset are we talking here?

To me, a few thousandths proud or a little more seems right to me. I want the barrel to sit square on the arbor.

If the barrel angles upwards then the barrel gap will be larger at the bottom than the top, and debris will be forced downwards to the arbor. Not that it wouldn't anyway. And also, the POI would be higher. I don't know how much any of that matters, but it messes with my idea of how mechanical things should assemble - they should fit together in their final positions without stress or strain with a locking key holding it all together.

 

[M. De Land]

Mostly just files and stones! And a drill press! So when I get the arbor touching the back of the arbor hole the wedge won’t go in. Also when you say start zeroing your number how is that done? Are you shimming behind the cylinder? I’m not sure if I’m understanding the process at this point. I would imagine that shimming more than a couple thousandths you would probably encounter problems with the hand functioning properly. Thanks kindly for the help! I did install an action shield the other day and it worked great. I copied it from photos I saw of the ones you installed! May do a cap post soon also. Not sure if it will be a necessity at this point. I don’t compete, but I still want the gun to function properly!

My education is deficient in various ways but I appreciate learning all the nomenclature possible.

What is a bearing spud?

Is a butt joint the contact between the arbor slot and the wedge?

“Barrel slots forward”?

Forever I have checked end-shake by placing on half ****, muzzle elevated and pressing down on the cylinder. That’s how, right? If the hammer is down may not the bolt potentially effect the measurement?

I used bearing spud at the front of the cylinder in place of bushing because it is more descriptive and I couldn't remember the technical term at the moment. Folks not familiar with the guns would most likely not know what the term "bushing" was referring to.
Butt joint is the interface of the arbor end an the arbor well bottom in the barrel. The wedge connects the two via the two barrel slots and the arbor slot.
Barrel slots are the two mortises in the barrel that the wedge fits through. When a wider wedge is built to move the barrel rearward often times the two slots on either side of the arbor need to be lengthened forward to provide clearance to draw the barrel up and close the gap at the breech..
When adjusting these points one must remember that an arbor needs clearance in the arbor well for it to freely move in and out of. This radial clearance remains as the wedge draws the barrel up which is another reason the arbor and it's well never become a single unite. These clearances most certainly flex and move when the gun is fired both from tension, compression of metal and torque from bullet rotation.
All of these movements are far more pronounced in open frame guns than in solid frame guns that don't have these clearances present when firing.
Colt made the 73 because it was a stronger design demanded by Army engineers not willing to except the weaker out dated designs of open frame guns. This was most certainly influenced by the solid frame Remington 58 design also being fielded in the Civil War.

 

[45D]

Let's see if I'm tracking with you:

**** the barrel to the side so the frame and barrel lug don't mate up.

Set up the arbor (adding or subtracting length as required) so it bottoms out at the correct endshake.

Now here's where I think differently.

You're saying the frame and cylinder lug will meet first, then the wedge pulls the cylinder back farther. How much of an offset are we talking here?

To me, a few thousandths proud or a little more seems right to me. I want the barrel to sit square on the arbor.

If the barrel angles upwards then the barrel gap will be larger at the bottom than the top, and debris will be forced downwards to the arbor. Not that it wouldn't anyway. And also, the POI would be higher. I don't know how much any of that matters, but it messes with my idea of how mechanical things should assemble - they should fit together in their final positions without stress or strain with a locking key holding it all together.

No sir. Do not " **** the barrel" to the side. It usually won't allow that "test" because the broaching of the wedge slot distorts the arbor hole to a more or less "one way" fitment. You generally have to dress the arbor to allow the "test" . . . so now you have a short arbor that has even more clearance!!! Why do that?
I've never ever "measured" for a spacer. It's a "fitted" item.

The wedge pulls the BARREL ( not cylinder) back against the frame and arbor. We're talking thousandths.
Typically when barrel/frame contact is first made, the barrel has a downward attitude. There is plenty of room to adjust the endshake. The barrel lug / frame contact is the "constant" or fulcrum for the barrel assy position. It's the arbor contact that defines the amount of endshake. Once established, the wedge can be driven in ( inducing
a LOT of tension) and you'll have the same revolver setup every time you reassemble it. The assembly will now react as a single structure rather than two assemblies beating against themselves ( without the tension generated by the wedge, they would rattle against each other which is what causes damage).

Mike

 

[45D]

Just to help you understand the design of the wedge connection, the forward side of the wedge contacts the forward end of the slot in the ARBOR. The back side of the wedge contacts the rear of the slot in the BARREL on both sides. Driving the wedge in then pulls the barrel assy rearward to bottom out against the arbor. It's a "triangulation" layout.
If the wedge is contacting the forward AND rearward part of the slot in the barrel, it's just a wedge in a barrel . . .

Mike

 

[Dude]

When I was first learning about these guns, the data I got was to rotate the barrel to the side and observe whether the barrel lug and frame line up evenly. Shim the arbor to make that happen. I don't do that now, except to see how far off the mating is once the arbor is shimmed.

How do you know when the arbor has bottomed out if the barrel isn't cocked to the side?

As an example, I just worked on an Armi San Paolo 1851 with a .035" endshake and a short arbor. The barrel lug and frame were mismatched by about the same amount. Perhaps this gun had been assembled with various parts lying around so nothing fit right. It was pretty gross. But the frame was too long. Removing the excess from the frame brought the endshake within limits at which time the arbor also bottomed.

Was there a different or better way to resolve these issues?

It seems simple now, but it took some thought to understand the force vectors of the barrel/frame/wedge.

I agree - having the arbor bottom into the barrel is the way to go from an engineering standpoint. But I don't see the necessity of having the barrel lug/frame mating much more than a relaxed fit (not stressed or loose). Firing forces want to compress that joint already, so there's no possibility of it opening up. Getting that connection to a point where it's not stressed takes some careful work, so I can see that in a lot of cases it's possibly best just left alone. In my case, I saw no other solution as driving the wedge in cocked the barrel quite a bit, left a big gap at the bottom of the forcing cone and still the endshake wasn't acceptable.

 

[45D]

When I was first learning about these guns, the data I got was to rotate the barrel to the side and observe whether the barrel lug and frame line up evenly. Shim the arbor to make that happen. I don't do that now, except to see how far off the mating is once the arbor is shimmed.

How do you know when the arbor has bottomed out if the barrel isn't cocked to the side?

As an example, I just worked on an Armi San Paolo 1851 with a .035" endshake and a short arbor. The barrel lug and frame were mismatched by about the same amount. Perhaps this gun had been assembled with various parts lying around so nothing fit right. It was pretty gross. But the frame was too long. Removing the excess from the frame brought the endshake within limits at which time the arbor also bottomed.

Was there a different or better way to resolve these issues?

It seems simple now, but it took some thought to understand the force vectors of the barrel/frame/wedge.

I agree - having the arbor bottom into the barrel is the way to go from an engineering standpoint. But I don't see the necessity of having the barrel lug/frame mating much more than a relaxed fit (not stressed or loose). Firing forces want to compress that joint already, so there's no possibility of it opening up. Getting that connection to a point where it's not stressed takes some careful work, so I can see that in a lot of cases it's possibly best just left alone. In my case, I saw no other solution as driving the wedge in cocked the barrel quite a bit, left a big gap at the bottom of the forcing cone and still the endshake wasn't acceptable.

Without any tension imparted at the barrel lug/ frame, it's going to vibrate itself bigger and bigger. Think about it, if a bullet is striking the forcing cone with 14K psi behind it and the force wants to rotate the barrel downward, the lug is the stop. Every action has a reaction. If there's no tension it's going to open up every shot. The wedge has to impart tension there as well as keeping tension against the arbor. Vibration is devastating if it's not delt with and that's the beauty of the design, it does it very well. Well enough to handle 23K psi loads.

For reasons already mentioned above, the "swing the barrel down" test is a useless exorcize. If you know it's already short, why do you need to prove it to yourself? Just make a spacer and reduce it until you get what you want. The clearances in each revolver are different and trying to measure the perfect spacer by measuring and then figuring out the clearancing that tension will remove when the wedge is driven in kills brain cells!! I can fit a spacer in less than 10 minutes without killing a single cell !!

Mike

 

[Dude]

I do agree with you there - tension is needed at the barrel lug when assembled. It can't be a loose or relaxed fit at that point. So I'm curious how much of a mismatch you've found to be acceptable or desirable. Or do you just not worry about it? It is what it is and go with it.

So your method of shimming is trial and error? Add a shim, assemble, measure, disassemble, thin the shim, try again. Ok, I get it.

 

[45D]

I do agree with you there - tension is needed at the barrel lug when assembled. It can't be a loose or relaxed fit at that point. So I'm curious how much of a mismatch you've found to be acceptable or desirable. Or do you just not worry about it? It is what it is and go with it.

So your method of shimming is trial and error? Add a shim, assemble, measure, disassemble, thin the shim, try again. Ok, I get it.

What do you mean by "mismatch "?
By the way, I don't use shim stacks. I did early on but that can fail. I've been using a single spacer the last 8 yrs or so, no problem whatsoever since.

Mike

 

[Red Owl]

I thought about .006 was about right. A lot of the tight gaps are for modern rounds with higher pressures and escaping gases, etc. Although the percussion should not "spit lead", a lot of them do and there is also more fouling than modern guns- a tight gap could lock up the action.

 

[45D]

I thought about .006 was about right. A lot of the tight gaps are for modern rounds with higher pressures and escaping gases, etc. Although the percussion should not "spit lead", a lot of them do and there is also more fouling than modern guns- a tight gap could lock up the action.

Since cap guns don't have a "defined" gap and the cylinder contacts the forcing cone every cycle, it is basically self cleaning. It seems to work best sending fouling down the barrel than out to the side. Makes them more efficient and gives the shooter a cleaner revolver.

Mike

 

[Dude]

By all accounts I've seen, a gap of .002-3" is the best.

What I mean by a mismatch is this: With the arbor bottomed a perfect match would be the barrel lug/frame joint match perfectly - not tight or loose. A mismatch would be when the barrel lug contacts the frame, the arbor hasn't yet bottomed. If there's a better way to describe this, let me know.

 

[SPQR70AD]

You DO bring them together . . . first . . . and THEN ( dress your spacer) find your endshake number.

That way, when the wedge is driven in, there will be Hugh tension imparted at the frame/ lug ( cause they meet first). The two assemblies will be under great tension . . . which is what you want.

Mike

do you make any u tube vids cause it is a little hard to understand the procedure when you explain it

 

[45D]

do you make any u tube vids cause it is a little hard to understand the procedure when you explain it

No but I can take some pics to explain.
I'll get some done today.

Mike

 

[Tizzy]

Dude is spot on in his responses. For what it is worth.. A method I have used instead of shimming...and shimming I have done,and does work (don't do this unless you don't have another option) is to braze to head of arbor some brass..then braze some more to the front of arbor where barrel wedge contacts. From there you can file for a perfect fit of arbor to frame, as well as appropriate wedge fit. At the same time you can establish appropriate cylinder gap. No slop left/right between frame and barrel assembly and appropriate gap established if done correctly. Just an option..that I know works. I hope it is a thought

 

[M. De Land]

Dude is spot on in his responses. For what it is worth.. A method I have used instead of shimming...and shimming I have done,and does work (don't do this unless you don't have another option) is to braze to head of arbor some brass..then braze some more to the front of arbor where barrel wedge contacts. From there you can file for a perfect fit of arbor to frame, as well as appropriate wedge fit. At the same time you can establish appropriate cylinder gap. No slop left/right between frame and barrel assembly and appropriate gap established if done correctly. Just an option..that I know works. I hope it is a thought

I wouldn't want brass as a check/stop surface to a hard steel wedge as it will batter out in short order just as brass recoil shields do in brass frame guns when to heavy of loading is used.. I have one now from a friend that has the nipple wells imprinted into the recoil shield and I can pull the barrel back and forth by hand the wedge is so short poorly fit in length,width and thickness. This gun also is showing puckered steel at the back of the barrel slots where the barrel gets a run at trying to go down range before the wedge stops the forward progress against the end of the arbor slot..

I thought about .006 was about right. A lot of the tight gaps are for modern rounds with higher pressures and escaping gases, etc. Although the percussion should not "spit lead", a lot of them do and there is also more fouling than modern guns- a tight gap could lock up the action.

Spitting lead (if it is lead and not un-burned grains of powder ) is caused by chamber barrel misalignment or improperly cut forcing cone, occasionally both.
Over large cylinder gaps will spit burning powder but seldom lead and especially if the cone corner at the breech is eroded or radiused.
One of the ways I have wanted to try to rebuild a brass frame gun is to make a recoil shield fly style cutter that uses the arbor for and axial and spring load it against the wedge with a washer for even cutting pressure. This will mill down the imprinted recoil shield square to the cylinder rear face . I would then make a steel bushing to the same thickness as what was milled off and sweat it in place with low temp silver solder. My guess is a new recoil shield surface of hardened, temper draw steel of around .050 thick would stop imprinting.
The arbor threads in the brass frame are what do the stretching and loosening with heavy load usage. An idea of a fix I have kicked around for this is a steel bushing sweated in and cross pinned into the frame for the arbor to thread into. A well executed sweat job into a stepped steel bushing edge would have tremendous shear load strength and would stop the arbor thread stretching in a brass frame gun.
Kicking around some ideas !

 

[1stnamebassist]

Well this has been a very confusing thread! Thanks everyone for the responses, it’s appreciated but it’s left me more confused than before! But I’ll try wording it different to see if I can get this figured out. Assuming my arbor is bottoming out, and my butt joints are butting up perfectly and my gap at the forcing cone top and bottom is perfect, how would I close up the cylinder gap? Let’s say without pushing the cylinder rearward it is around .013, and when the cylinder is pushed rearward at halfcock it is about let’s say .002 to .004 more, how do I close up the cylinder gap? I think I need a picture book or I’m getting too old to understand what everyone is saying!

 

[M. De Land]

Well this has been a very confusing thread! Thanks everyone for the responses, it’s appreciated but it’s left me more confused than before! But I’ll try wording it different to see if I can get this figured out. Assuming my arbor is bottoming out, and my butt joints are butting up perfectly and my gap at the forcing cone top and bottom is perfect, how would I close up the cylinder gap? Let’s say without pushing the cylinder rearward it is around .013, and when the cylinder is pushed rearward at halfcock it is about let’s say .002 to .004 more, how do I close up the cylinder gap? I think I need a picture book or I’m getting too old to understand what everyone is saying!

What has worked for me is to make a wider,heat treated wedge of tool steel and turn down the lower barrel lug in my lathe. This moves the barrel rearward square to the cylinder face an coaxile to the bore . The gap is measured with a feeler gauge to check square as well as gap closure. Once the gap is closed and even then I have various thicknesses of steel shim stock to make a single shim for end fit of arbor. I don't use shim stacks either for the final spacer or threaded adjustable stops.
I do not care for drilling , tapping or removal of any steel from the end of the arbor for adjusting wedge width( make a new one that fits just like Colt invented) except to dress it even.
Concerning wedge fit I want as much of the wedge surface as I can Diakem spot fit to the slot in the arbor to check barrel separation. I make the wedge thickness as well (as width and length) fit both barrel slots and arbor slot snugly.
I don't believe a wedge is supposed to be pounded into the slots overly tight, it should fit them and a bump from a screw driver handle is sufficient to keep them in place if fitted correctly.
Here are some photos I took of new wedge making, heat treating, fitting and barrel lug removal.
Note how the new wedge fits the slots in thickness, at the rear of the barrel slots and the necessary clearance at the front of the barrel slots. Except for the clearance at the front the wedge should look like it grew in the slot in my opinion.
A wedge so made and fit will not batter, deform or pucker barrel slot metal.
Another photo of interest is the last one of a safe file ( it only cuts the slot forward) ground to extend the barrel slots forward for draw up clearance.

 

[M. De Land]

What has worked for me is to make a wider,heat treated wedge of tool steel and turn down the lower barrel lug in my lathe. This moves the barrel rearward. The gap is measured with a feeler gauge to check square as well as gap closure. Once the gap is closed and even then I have various thicknesses of steel shim stock to make a single shim for end fit of arbor. I don't use shim stacks either for the final spacer or threaded adjustable stops.
I do not care for drilling , tapping or removal of any steel from the end of the arbor for adjusting wedge width( make a new one that fits just like Colt invented) except to dress it even.
Concerning wedge fit I want as much of the wedge surface as I can Diakem spot fit to the slot in the arbor to check barrel separation. I make the wedge thickness as well (as width and length) fit both barrel slots and arbor slot snugly.
I don't believe a wedge is supposed to be pounded into the slots overly tight, it should fit them and a bump from a screw driver handle is sufficient to keep them in place if fitted correctly.
Here are some photos I took of new wedge making, heat treating, fitting and barrel lug removal.

A few more of the heat treating process of a wedge made of A-2 tool steel. It requires two stage heat treat and must be wrapped in tool wrap to prevent scaling. The paper in the first picture burns to ash inside the stainless tool wrap and seals out all oxygen.
The second picture is the wedge sealed up and ready for the heat treat. The whole process along with drawing the temper takes several hours with A-2. I also use a lot of O-1 tool steel for pins etc that do not require as much warp free precision do to the part shape.
I hope the pictures make the process a bit more clear for you!