barrel/cylinder gap fix?

[treebeard]

on my uberti 1851 revolver there is virtually no barrell/cylinder gap. The cylinder face has rub marks over a portion of the face.
So how best to get a small clearance? I fit the wedge so the spring hook barely snaps over the far side. I will appreciate any help.

[greyhawk]

on my uberti 1851 revolver there is virtually no barrell/cylinder gap. The cylinder face has rub marks over a portion of the face.
So how best to get a small clearance? I fit the wedge so the spring hook barely snaps over the far side. I will appreciate any help.

Coffinmaker will likely come along directly but in the meantime search out Larsen E Pettifogger (google if you cant find it here) he did a series on cap guns and also a ten page writeup in feeding dynamics in the toggle link rifles - good stuff all ot if . 

[Pettifogger]

Before you conclude there is no cylinder gap grab the cyllinder and pull it rearward.  If it moves that is your cylinder gap.  Remember we are only talking a few thousands of an inch.  The Navy does not have a cylinder bushing so the hand spring can and does push the cylinder forward until it is stopped by the back of the barrel.  Normal.  If you cannot pull the cylinder back at all and it is genuinely binding on the barrel remember that it is a Uberti and virtually all Uberti arbors are fitted incorrectly.  The solution is to add material to the front of the arbor or make a spacer and then fit the arbor to the barrel.

[Coffinmaker]

PLUS ONE to Larsen E. Pettifogger.  If you haven't corrected the Barrel to Arbor fit (See Larsen's tutorial) your going to get a bunch of drag on the front face of the cylinder.  As Larsen pointed out, the hand is going to push the cylinder forward which is normal.  Without correcting the Barrel to Arbor fit, you get a different fit and gap every time you take the gun apart.

[riflee]

Once that forsaken danged arbor is housed up well the breech end of the barrel can be faced with a piloted reamer and gap set to whatever a person wants. One thing.....buying the tools is cost prohibited so finding a gunsmith would be the way to go. The little bit of reaming shouldn't cost much. Forcing cone check and ream (maybe) would be minimal too.


I remember a time when people would be talking feeler gauge settings for cylinder gaps and not "bottomed arbors".  Having bottomed arbors just sorta bloomed out there like a big patch of tulips in the spring. I imagine it's very refreshing for a lot of people when they get those danged bottomed arbors.


Having those CNC machines at Uberti sure could do the task.

[greyhawk]

Once that forsaken danged arbor is housed up well the breech end of the barrel can be faced with a piloted reamer and gap set to whatever a person wants. One thing.....buying the tools is cost prohibited so finding a gunsmith would be the way to go. The little bit of reaming shouldn't cost much. Forcing cone check and ream (maybe) would be minimal too.


I remember a time when people would be talking feeler gauge settings for cylinder gaps and not "bottomed arbors".  Having bottomed arbors just sorta bloomed out there like a big patch of tulips in the spring. I imagine it's very refreshing for a lot of people when they get those danged bottomed arbors.


Having those CNC machines at Uberti sure could do the task.

Pettifoggers plan is better ! Theres guns out there that if you bottom the arbour without a washer or something in there the barrel gets all skewed upwards and the cylinder wont fit - ream the barrel face to get clearance and its still a stuff up
Yeah Uberti could do it if they wanted - but the equipment would have to be reset - a whole bunch of stuff to do to get it right - they sellin hundred dollar guns out the door as fast as they can move em

[Coffinmaker]

Actually, fixing the problem is really not all that difficult.  Should have been fix'd years ago.  Since customers continued to buy a faulty product anyway, why bother??

Pietta Open Top guns come out of the factory with 99.99% Barrel to Arbor fit.  IT AIN'T ALL THAT HARD!!

[greyhawk]

Actually, fixing the problem is really not all that difficult.  Should have been fix'd years ago.  Since customers continued to buy a faulty product anyway, why bother??

eeezackly! - but I bet they got an armload of excuses along the lines of - too hard - gonna cost money

on another track entirely I have a browning model 71 winchester copy - everybody raves about the build quality of the japchesters - mine was purty as could be on the outside - but they FORGOT to machine the hammer clearance arch on the underside of the bolt (just mine or how many in that run? who knows?) - I had winchesters all my life but never a new one - yeah it will smooth up after a bit of use - hell no! there was an eight inch of steel where there should be NONE! - that aint gonna smooth up! - then the inertia firing pin failed to ignite right when an alaskan brown bear was in mid charge - that sucker chewed my head right off and spat bits on me all over the landscape - damn lawyer safeties! - well when I recovered from that little escapade and pulled the gun down to fix it was when I figured that bolt was not finished being machined - lookin at it beside a 92 bolt helped - then I found me some pictures on the net of 86 bolts - so much for browning / miroku quality.   

Pietta Open Top guns come out of the factory with 99.99% Barrel to Arbor fit.  IT AIN'T ALL THAT HARD!!

[riflee]

Coffinmaker ain't lying. I ain't that difficult to get an arbor bottomed correctly. There's multiple ways to do it...take yer pic.

Weld and finish file the end of the arbor.......drill a hole and screw a brass or steel button to the end......have a new arbor made by a machinist......use a shim in the bottom of the barrel hole(my favorite)......buy Pietta and hope fer the best.

I like the shim method because it's cheap and doable by most anyone. Get a little fender washer from the hardware store that is about the right fit in the hole. Get it a little big diameter wise. File till it fits snug enough to stay in the bottom of the hole so it doesn't get lost. Next take a stone and take the shim(fender washer) down to the right size. Use grease or Prursion Blue to put on the end of the arbor and seat the barrel. Then  look at the end of the arbor and in the barrel hole. Close is when there's blue on the bottom of the barrel hole and the end of the arbor. Done is when the blue is crushed and moves off the right surfaces(end of the arbor and around the edge of the barrel hole). It depends on how the bottom of the hole is drilled where it can be concave or flat down in there.

The crush fit from the fit being supper tight from the force of the wedge is what will remove all color from the spots where it fits right. 

The idea is to get a good bottoming of the arbor simultaneously when the barrels bottom lug is tight to the frame.


Then then you try the cylinder gap visually or with a feeler gauge. You see.....bottoming the arbor doesn't exactly fix-fit the cylinder gap. The gap may be too tight which is the better of the two scenarios of too tight or too loose. You see, bottoming the arbor can lessen a cylinder gap or widen it. The gap you have to begin with may change when the arbor is bottomed nice and tight.

First scenario.....A gap that is too tight merely needs the breech end of the barrel filed or reamed to specification. That's whatever you want from .001 to .006 of an inch or more. Less is better most people will tell you. Some Hombre like wide gaps though.


Second scenario.......A gap that is too wide. That takes a regular bonified gunsmith or a regular bonified Kitchen Table Gunsmith that has experience in that fix. The bottom lug of the barrel needs taken down carefully until the cylinder gap is correct in it's specification. Some might add that they like to take a little off the end of the frame.  That means removing the frame locator pins and that gets you in trouble some times. Mess up and a frame is more difficult to replace than a barrel.

Now...... that can be a little tricky but not outside the scope of someone that has confidence in their file use or drill table use or milling machine use. I use the file or the milling machine use to take a little off the barrels bottom lug till the cylinder gap it good to go when the barrel is against the frame and the wedge is set in the barrel.  Now......


If you have a milling machine the cylinder face can be milled down ever so slightly to set the cylinder gap if the gap is too small.  There's always some aggravation to this Colt fix it time. It's usually better to find a forum where there are fix it cowboy gunsmiths that can take care of the bottoming of the arbor when the going gets tough. I know.....been the many times. When the job is done and right on it's rewarding. I like that feeling. Then I voluntarily admit myself into an insane asylum for a period of time. Thing is...once they let you in they want to keep you forever    That's is when you fight your way out and then join the Foriegn Legion and hide away for a decade or two.


You see....for instance.  When the barrel needs set back to fix a cylinder gap ,and that gets done, there arises another aggravation. What might that be?

Making a "new" wedge to fit the barrel/arbor slot once the barrel is set back and lengthens it is what is needed. That is where you get innovated and make a new wedge with a file or weld the edge of the original wedge and file it nice and fit again or make a new wedge on a milling machine or a good drill table using a mill table that can be put on a drill table. You know...use end mills to mill out a new wedge.


I guess the cylinder gap thing can get tricky but.....the scenario where all is needed is a shim or whatever to fill the gap between the end of the arbor and the bottom of the barrels arbor hole is the most likely one to happen and the easy one to take care. The hardest part of that is to shape the diameter and stone the shim thickness to fit the gap.   This is when the cylinder gap is already in specification.


I guess it's all in the luck of the draw when you buy whether it be Uberti or Pietta. I'd guess if the manufacturers were convinced the bottomed arbor is what is right and defected guns without that is what is not right. then people decide it just ain't worth the trouble to buy defected guns so they buy a new bowling  ball instead of a gun.......sales would drop off.

[treebeard]

Thanks to riflee for the extensive response.  At this point i have worked fitting the bolt so it does not mar the locking notch on the cylinder.
the Pettifogger article is a big help. Once assembled there is no barrel cylinder gap even when i put back pressure on the cylinder. So looking at the various means outlined by riflee i am going to try the washer route. i am not going to fire this revolver till the gap is fixed.

This experience has made me curious about whether or not if the Colt reissues or Signature series are better fitted or even if the old Centaure's out of Belgium are any better. Any input on this??

Thanks again for the help as i get this revolver functioning.

[45 Dragoon]

Treebeard, nope, they  all  have short arbors. Only Piettas  for about the last dozen or so yrs. have "fixed" the issue. They're a little on the large side of clearance for me but it's easy to get to my spec. Of course the original Colt open top revolvers were correct. Never have delt with a Centaure but I wouldn't be at all surprised if they had short arbors as well.

Mike

[Coffinmaker]

What the Dragoon said.  I have never personally run into a Uberti built Open Top that was correct.  None.  Because of that, I have also never run into second generation nor signature Colts that we're correct.  We must remember, the second and signature Colt guns were built from Uberti parts.  Short Arbor is Du Rigger. 

TREEBEARD:  There is a quick temp fix.  Drop by your local Lowes and pick up a package of 5mm split washers (I prefer stainless).  Drop one down the hole of the Barrel lug, square it up and shove in the Arbor.  About 95% of the time, the split washer will make the Barrel to Arbor fit.

There is a problem with the Barrel to Arbor fit.  Normally, the bore of the Barrel Lug and the diameter of the Arbor don't match either.  The Arbor simply binds in the bore before it can bottom out.  This binding also makes it very difficult to check the Barrel to Arbor depth.  You can make a simple "flap Sander" to eliminate the burrs in the bore (it's a Uberti, there ARE burrs).  Then, With the frame in a padded vice, polish the Arbor with 350 Wet/Dry (Play shoe shine all the way around) until you get a nice slip fit.  Then fit the Wedge.  At the end of this goat soap, you will probably find the Cylinder now has acceptable Barrel to Cylinder gap.  Barrel Breach will have sharp edges, polish those and polish the barrel breach flat so it doesn't score the cylinder face.

Then ..... Replace the OEM nipples with Slixshot nipples.  Replace the Main Spring with a lighter Main Spring.  Wolff, VTI and Lee's Gunsmithing all have very nice reduced Main Springs.  Also replace the OEM Trigger Bolt Spring with a reduced spring to keep the Bolt from hammering the cylinder slots. 

At this point, you'll have a really nice start.  Yep, there is a bunch more can be done.

Or > > > > > Find somebody that wants a Uberti and then start over with a Pietta   

[treebeard]

I have now bought my last Uberti open top!!  Thanks for the 5mm split washer suggestion.  I will keep working this revolver to see how far I can improve it. It 's a good learning experience which allways good.

[riflee]

Howdy treebeard this is for you.

Don't put a washer in the bottom of the arbor hole to set the cylinder gap. That may make a space between your barrel and frame and make your wedge too tight to go back in.  You put a washer in there whereas it fills the space at the end of the arbor but leaves the barrel against the frame. You know.....when the arbor bottoms the barrel is against the frame.


If you are steady and have a good grip you can take a little off the breech end of the barrel with a file. You can hold the barrel in your hand and turn the barrel every few strokes of the file so you don't get too far off with the face of the breech end crooked(not concentric with the bore). That supposedly is how old 19th century rifle makers did the ends of rifle barrels. The old saying used to be a gunsmith was described as a good one by saying ,"he's good with the file". I can do the job well with a file but I wouldn't say I'm a gunsmith. A gunsmith is someone that knows most all there is to know. I still have a few million things to know to catch up. One thing that is nice about not knowing everything is there is a good satisfying reinforcement to thunkin up or learning something new. Even more satisfying if you put the new learned thing to good proper use. I love it when I've been doing something a certain way for years and then....BINGO.....I suddenly thunk up an even better way to do something.


You see.....at one long time ago if I wanted my barrel to stay put on the arbor and give a consistent cylinder gap I painstakingly fit a shim into the arbor hole on top the arbor  (figured somehow the best space to fill was on top I guess because that is where the barrel space was taken up or closed when the wedge was put in and the barrel canted down to meet the arbor and fill the space) to make  a tight fit there. It's tricky to get a shim to slide in where it's making a tight fit. The shim can't stick out or it may rub the cylinder. Of course if the shim rubs the cylinder it gets bent upward a little and rubs the cylinder some it helps keep fouling out of the cylinders center hole. Wonder upon wonder. That could give people some ideas I bet.

Anywhoooo.....somewhere along the yellow brick road I went to the "bottomed arbor thing" and never looked back. No wait.....I do look back since some of my many cap&baller Colts still have the shim in there at the top beginning of the barrel arbor hole. The shim goes in on top the arbor about almost a half  inch sometimes more. The wider the shim is the tighter it is so it can be adjusted with a dinky ole pair of scissors. That is pretty close to having a tight arbor hole and a consistent cylinder gap because of it. When there is a shim in there it's not a good idea to think about changing out cylinders for full ones out in the field.


I have a little job going to put together a nice brass framer Colt from all odd parts. It's together and timed and aligned and tuned enough and all but....what I want to say is that the CVA KIT barrel I'm using is a perfect tight fit on the arbor so the gun doesn't need a bottomed arbor. The barrel is tight but not so tight it can't come off without tools. I just use the loading lever and the plunger to pop the barrel off once the wedge is out of course.  

One kindly thing about this gun I'm putting together is....the arbor on the brass frame went in the barrel and was perfectly bottomed right off the danged bat. I had to take a piloted reamer and set the cylinder gap a little though. I did a .006" gap. I like that size. I've heard that a gap of  .001" lets less fouling thru thus puts less fouling on the face of the cylinder. I'm not sure that makes sense because such a tight cylinder gap takes less fouling to start rubbing. All things being relative. I'll try it out on some other gun later I guess.
I think I mentioned somewhere else recently that I've kind of taken to putting a small weld on top the arbor right where the barrel hole begins (extends in under the barrel a ways) and then file it to shape to make a good tight fit there. That works to make a consistent cylinder gap too. The barrel can not cant down to fill the space if the space is not there after a weld spot is stuck there. If there's is a weld to tighten things up there at the beginning of the barrels arbor hole and there is also a bottomed arbor that is the deluxe model barrel fit. That is the best way I guess except for a good snug fit of the arbor to  the barrel hole. You don't need a bottomed arbor with that. I wonder what the original Colts had. Snug arbor to barrel fit or bottomed arbor or both. I say it was probably both. 


Man.... I've been running my mouth-key board again.   If the manufacturers put the danged bottomed arbors to the guns I could retire.   Wouldn't hurt for them to tighten the arbor holes either.  They could put a little description in the directions on how to pop off a barrel with the loading lever.

I couldn't even imagine what they would say in directions about how to get wedges out of new Colts(Pietta). I should email them and see if they might put a little cant on the inside of the wedges spring end so it doesn't hook the wedge to the barrel even more.  Maybe I'd tell them to get the wedges out once after force fitting them in with some sort of 10,000 lb. press or whatever.

[riflee]

This string of post's could be helpful to a person new to cap&ballin and bottoming arbors and cylinder gaps and all that. That is the name of the game so to speak. Being helpful and supporting to the cap&baller revolver fraterity. 

[Coffinmaker]

Oh Good Grief   

Riflee ...... What on earth are you talking about??  Nine paragraphs of gobbled gook that don't really address anything??  The first step is to fix the Barrel to Arbor fit.  You can't do ANYTHING else until that fit is a close as you can make it. 

NEVER, EVER attack the breach end of the barrel with a file or machine until the ARBOR FITS.  Using a split washer in the Arbor Bore is NOT to fix barrel to cylinder gap.  It is to fix the barrel to arbor fit.  The first step in fixing the barrel/arbor fit is to de-burr the inside of the arbor bore in the barrel.  Then cleanup the arbor to a nice slip fit in the bore.  Until you can turn the barrel on the arbor to see how much it over-runs the frame end, you're chasing your tail.  THEN the split washer is a quick, simple, cheap way to get correct barrel to arbor fit 99% of the time.  No machine tools necessary.

Once the barrel/arbor fit to a solid bottom at the same time the barrel contacts the frame, you WILL have to re-fit the Wedge.  It's basically like a line of dominoes.  Unless you start with the first domino, you'll NEVER complete the line.

[riflee]

Coffinmaker,

If I make the effort typing some things you might save the criticism for after you read carefully.  Being a "gun plumber" you already know it all.  I try to help the un-advised with their cap&ballers.

Go back and research for "Rifle" post and you may find I was like the tip of the spear putting out the word about bottomed arbors. I saw no explanations about bottomed arbors before I began. I put forth a lot of effort typing about it over and over. Give me a little credit for effort at least.


You're correct to say the barrels hole needs cleaned and smoothed. That's how it begins to be able to turn the barrel ninety degrees to twist it over to the guns frame to see where the arbor is in relation to the bottom of the barrels hole. That little simple effort is how I explained to folks wanting to know how to tell how far the end of the arbor was away from the bottom of the barrels hole. Now I stumbled across that little trick when I wanted to know and found out my two new Pietta revolvers actually had bottomed arbors.


That idea of bottomed arbors is something I put a lot of effort into spreading to folks via the net.  Putting forth the effort to try to be a help to folks. Once I saw the idea was being spread I backed off the computer stuff due to disability that makes it difficult to type.

People like you take up the cry and continue to help folks. The cap&baller fraternity is full of honorable people willing to help further the knowledge to have to "fix" some problems with what some refer to as "kit guns".

My crusade started with promoting the proverbial lube pill/lubed wool wad "under the ball on the powder".  That spread well. It's common knowledge now just like the bottomed arbor thing.  Now.......I don't know if I have the energy to promote the idea the snug arbor is "the thing". You know...snug in the barrels arbor hole.  The snug arbor in the hole "and" the arbor bottomed is the ultimate set up. Of course that mandates for a machinist to turn out that precise arbor part. A "Kitchen Table Gunsmith" can use a small weld or copper shim in the right place in conjunction with the bottomed arbor and forgo the cost of having a new arbor machined.


The best would be a new well fit arbor ,I suppose, and would be emulating the fit of the original Colts I'd guess anyway.


Anywhoooo....... I have to raise a cheer for all the folks that take the effort to be a help to, "The Cap& Baller Fraternity".  People like you for instance Coffinmaker.

A hearty hand shake and a firm "thank you " to all those helpful folks" from ole simple man "riflee".  Carry on with your "sound wisdom" folks!   Salute!

Oh!  I'm well aware of the fact the bottomed arbor comes first and foremost and try to promote that. After that there inveritably comes the chance a pitoted reamer may be needed to set the cylinder gap precisely with the breech end of the barrel ending up concentric with the centerline of the bore.

I try to promote the fact that an arbor with a snug fit in the barrels arbor hole is a step above the bottomed arbor mechanically speaking. The bottomed arbor with the snug fit diameter wise in the barrels hole...That's the ultimate.

I just try to get the idea across that if the arbor is a snug fit in the barrels hole the arbor need not be bottomed. I've proved that with my own Colt cap&ballers and with others guns I helped with. It's true believe me.  Once that small gap between the arbor and the top of the very beginning of the barrels arbor hole is closed by the wedge force the cylinder gap stays constant just like with the bottomed arbor. That contact point where the top of the barrels arbor hole meets the arbor is where the consistancy is created.  Of course that gap should be very small to begin with.

That's where the snug arbor in the barrels hole is important. I've learned to forego the "new arbor that fits well" by using a thin strip of shimstock to close that gap. I'll tap the barrel over the shim that is on the arbor at the beginning of the barrels hole with a rubber or nylon hammer.  When I do that the barrel is tight on the arbor and the loading lever is needed to pop the barrel loose. It's not something that would be done out in the field though.  Might loose the thin strip of shim. Of couse the shim can be soldered to the arbor if the cylinder can go over it.  It would be easier if a new arbor was turned out that fit the barrels hole snuggly. Been there done it both ways. Shim or new arbor. Take yer pick.


When a person buys a new Colt cap&baller and it already has a snug arbor "and" the bottomed arbor that is just capital. Best way to go.


Anywhoooo.......thanks to anyone who takes the time to read this gobbled gook!

[Slamfire]

Back in the day ,( cough,Choke )when i buy'd ( obtained ) my OT 72,, l came straight to this forum,, met MR. Coffin and a couple of others,, " split washer's ,,they said ",, I buy'd ( obtained ) 6 ,,2 are under my work benches some where,,used 1 on a bolt,,put 1 in the arbor hole,,tied a string on 1 and hung it up on my wall, ,, maybe I only buy'd ( obtained ) " 5 ". But it "worked,, for me & my OT" quick, fast,and in a hurry,, end of story. 

smoke'm if ya' got'm,, Hootmix

[greyhawk]

Coffinmaker,


I just try to get the idea across that if the arbor is a snug fit in the barrels hole the arbor need not be bottomed. I've proved that with my own Colt cap&ballers and with others guns I helped with. It's true believe me.  Once that small gap between the arbor and the top of the very beginning of the barrels arbor hole is closed by the wedge force the cylinder gap stays constant just like with the bottomed arbor. That contact point where the top of the barrels arbor hole meets the arbor is where the consistancy is created.  Of course that gap should be very small to begin with.

I am sorry Riflee but that above is not really making sense to me, perticularly the first sentence of it
You are promoting an interference (jam up) fit of the arbour rather than having it correct length and bottomed - nope I go with Coffinmaker on this.

[riflee]

greyhawk, that's alright. The bottomed arbor will do the trick. There are other ways to make it work though. You have to see that a bottomed arbor that is a close diameter to the barrels hole is beneficial.

A bottomed arbor in a loose hole can and does still cant a little down and back when the immense force of the wedge is applied.  The arbor will bottom and then since it can't move past the frame at the barrels lug the force will make whatever is loose close up. That loose is always at the top of the beginning of the barrels hole. The barrel will move till it closes that gap. That takes the perfectly bottomed arbor and makes it contacted at the top end of the arbor and opens at the bottom end of the arbor.  That's all I'm trying to say mostly.


That gap at the beginning of the barrels hole between it and the arbor will most always close with a bottomed arbor. The arbor will still be bottomed but will loose some contact with the end of the barrels hole. Happens most always unless the arbor is a perfect fit in the barrels hole. There's always going to some looseness when the barrel goes on the arbor and can only be remedied by minimizing the fit since if it fits too tight it is too difficult to go on and off. Sooooo.....the best is the fit of the arbor in the barrels hole as snug as possible and still get the barrel on and off easy enough.


It's not complicated or anything it's just that a barrel too loose on the arbor diameter isn't good. The person understanding the bottomed arbor is good should know the snug arbor fit in the barrels hole in conjunction with that is better. That's what I'm trying to get across.


I've proved to myself anywhoooo that an arbor that is a real precision  fit in the barrel hole makes the bottom arbor unnecessary.   

Using a tight arbor and working it in with the file and diamond compound makes fer an arbor with a very close fit in the barrel. Difficult to get on and off till the compound does it's thing and the space between the arbor and the barrels hole is as minimal as possible like the barrel can't move any on the arbor. 

If the barrel can't move any sideways or up and down on the arbor when the barrels bottom lug meets the frame things stop right there. Consistent cylinder gap will be there without the bottomed arbor. Therefore the bottomed arbor "and" the minimized space between the arbor and the barrel is the best.  That's all I'm saying. Maybe I'm just not saying it plain enough. It's impotant to know you don't want a barrel too loose on the arbor.


Using a split washer for bottoming an arbor?  Split washer is spring steel and "split" to apply pressure. Split is uneven contact of the arbor to the bottom of the barrels hole.  Unless the split (lock washer) washer is compressed till it is pressed flat there isn't a truly bottomed arbor. It would be like a spring loaded bottomed arbor. Therefore the wedge could compress the split washer more or less each time the wedge is put in and snugged up in the slot. That could make for a varying cylinder gap.


A split washer being the shim/bushing in the bottom of the barrel hole couldn't be a cure all for all un-bottomed arbors. It would be too thick for some applications and too thin fer others and a spring fit for others. Know what I mean?  Just my opinion and sadly I'd have to admit I don't know it all. Myself being like that makes it all that much more rewarding when I learn a new trick. 


All someone can do is take what they think works and use it.


Anywhooooo....I'm not promoting an interference fit-- jam up. I'm promoting a "precision fit". Precision fit is a little more loose than an interference fit. Now putting a piece of shim stock on the arbor and getting it in the barrels hole on top the arbor  "is" an interference fit. I'm trying to say that makes a tight fit of the barrel on the arbor and then the bottomed arbor isn't needed.  I just use that example to show what a good snug fit of the arbor in the barrels hole does and or remedies. 


If you were blue printing a Colt Open Top like doing a close tolerance race motor then the tolerances would be tight and close right?


I have to put this out there to get something I'm saying across. Take an Centaure Centennial 1960 New Model Army "Belgian" 1860 Army cap&baller for instance.  Some of them had an interference fit with a slight taper to the arbor where it was at the beginning of the barrels hole. Half an inch or so into the hole that had the "same degree of taper".
They did that precision enough so that the barrel went on the arbor and stopped exactly where the barrels bottom lug was against the frame and the cylinder gap was set. That set up was very precision and...... when the wedge was inserted the barrel did not move on the arbor with any looseness at all. No looseness interference fit with the taper to the arbor and the taper to the beginning of the barrels hole and .........no bottomed arbor. That was a consistant cylinder gap fit and with that taper the barrel didn't move on the arbor sideways or up and down or anywhere even where the arbor was past the taper and a little loose in the barrel hole.


That was an interference fit that was actually more stable than a bottomed arbor would be.  That set up wasn't on all the Belgian 1860 Model Army  revolvers I've worked with. I expect that was due to the trouble of doing that taper to the arbor and the barrels hole so the barrel stopped right where it should. It's a real good set up though since the taper would facilitate the barrel coming off easy.   


Therefore myself ,"Kitchen Table Gunsmithing", before I knew better I could create the same type set up struggling to learn to set the right thickness shim stock being the right width into the barrels hole on top the arbor about an inch or so in the hole and have a consistant cylinder gap and all.  That was sorta emulating the Belgian Colt before I knew there was such a thing with a tapered arbor. I did wish I had a lathe to make arbors with that  taper but....back then working at the kitchen table the shim stock thing did the job and worked well.  Some of my old cap&ball revolvers still have the shim in them. I don't even know how many I have now stashed away here and there. 20-30 maybe.


I know one thing.....the way some of the Belgian Army Colts were with that tapered arbor/tapered barrel hole was a thing of beauty.  That may show some Folks how a precision fit arbor in the barrel hole can be a good thing.


Of course hardly anyone is going to go beyond the very capable "bottomed arbor" since not many Folks have a lathe or the money to pay a Gunsmith with one to make a new arbor for their gun. So maybe just understanding a little more about the "arbor thing" just may be a little interesting for some Folks.  I do know fer sure that an arbor that is bottomed well AND has a "minimal close tolerance in the barrels hole fit" is....the best.  Of course.....one may ponder some on the tapered arbor/tapered barrel hole interference fit set up too.  The Belgian gun manufacturers did.