Setting B/C gap on Open Top Colt

[Navy Six]

Enjoyed the recent post on arbor shimming. My question is how are you setting the b/c gap if the arbor is now bottomed out in the barrel? You must be removing metal from somewhere(barrel lug?) to close the gap to .002 as 45 Dragoon suggests. Of course, I assume this is done prior to any adjustments to the arbor/barrel relationship.
I have always gone with the usual suggestion to keep the b/c gap at about.008-.010 for these blackpowder guns and when I have previously adjusted the arbor on a bunch of Ubertis' they pretty much have fallen within this range. But recent discourse from 45 Dragoon makes me think a tight b/c gap can work. By the way, all I shoot is blackpowder.

 

[45 Dragoon]

Navy Six,
Material is added, not taken away. The problem is a too short arbor. What you do is fill in the space by bringing up the bottom of the arbor hole to meet the arbor (the correct way IMO) or adding material to the end of the arbor (What?!). The arbor length is what defines the barrel/cyl clearance. So, by "correcting" the arbor fit, you are (at the same time) setting the bbl/cyl. clearance.

You say you keep the gap ( it's a clearance since there's no bushing) at .008"-.010". How so? By the depth of the wedge? That's called a loose wedge. If the wedge doesn't preload the mating of the two assemblies, it's a loose fit. I always say to tap the wedge in, no " finger tight" stuff. Finger tight won't preload anything. It will sound and feel solid when it "seats".
The wedge isn't a " clearance " setter. It's sole job is to hold the two assemblies together (under load so it won't loosen). Generally with an Uberti, the barrel will close against the cylinder and lock it up. Pietta has made great strides in there open tops and latley, the arbor bottoms out with a fairly decent bbl/cyl setting .Usually, all I have to do is "fine tune" it to my spec.(.002".)

The .002" spec I use "works" (as it has for years) because almost all of the fouling goes out the barrel and less out between the barrel/cyl. Theoretically, less pressure loss equals more vel./energy (measurable or not). You can in fact feel "better" recoil. The other benefits are - a much cleaner revolver after a day of shooting, - all day shooting with no binding so no need to break it down while at the range (or wherever) and the ability to set the open top to be dry fired since the cylinder can't move out of "range".

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

 

[Navy Six]

45 Dragoon, yes, I have been "filling the arbor hole". When done, the arbor and barrel are locked as one solid piece and the wedge is fitted to a slight friction fit where a light tap is required to seat it. The wedge spring just barely protrudes from the right side of the barrel--enough for the spring "nub" to clear. At that point you really can't drive the wedge in any further, so the b/c gap is kind of set. I don't utilize the wedge to set the gap as I realize without fixing the arbor relationship the wedge will move with wear or by pounding it in too far. So at that point, IF the b/c gap is too large(I should have clarified that in my original question) what do you do?
I think part of the problem with recent NIB Ubertis' is that now the arbor is fitted too tightly(into the arbor hole)and still not bottomed out. You are fooled into thinking the arbor is bottomed out when it isn't. In the last couple of years I've purchased several new Uberti cap & balls and had a real time getting the barrel off right out of the box because of the tightly fitted arbor.
By the way, not picking on Ubertis here. I have a Pietta 51 Navy made in 1996 and that had the shortest arbor of the whole bunch.

 

[whughett]

Other than an excessive cylinder gap affecting cap ignition what other effect could the cylinder gap have, assuming the wedge is in effect holding the barrel frame together tightly. Which in my case was the problem on an 1860 Army.
Temporary paper shims has solved the loose barrel problem but now there is a slight fore and aft movement to the cylinder. Slight but there is movement. Gap is in the .030 range. I am guessing the is indeed excessive

 

[robhof]

robhof

As 45 Dragoon has said previously, the larger gap allows more fowling out around the arbor and face of the cylinder, enough to cause seizing of the cylinder, requiring stripping and cleaning, also reduced pressure through the barrel/lower fps for the projectiles. Steel washers are cheap, durable and come in a large variety thicknesses and can be mixed and matched to proper fit and then glued to the arbor end for a permanent fix.

 

[45 Dragoon]

Robbof, very well stated, thank you. The only change I'd make is where. I bond the shims (washers ) to the arbor hole. I don't believe in adding to the arbor. It's just my preference.

Mike
www.goonsgunworks.com
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[BCRider]

If the arbors are wedging into the holes like that it must make the barrels extremely hard to remove. If they are not bottoming out perhaps it's some deformation or burrs at the wedge holes that are producing the early tight spot. One would likely want to use some blueing and check for scuff marks after setting and removing.

From the sounds of all these open top threads it sounds like some guns are sent out with a "proper" seated fit and others are sent out with short arbors. The "proper" from the last sentence meaning that the arbor bottoms out in the barrel's hole, not that it's necessarily the optimum fit as delivered.

 

[noelf2]

So on an open top colt, like a 1860, should the barrel/cylinder gap be .002 at full cock, or with the hammer down? The hand pushes the cylinder closer to the barrel at full cock.

 

[ZVP]

Is a larger B/C gap needed for conicals?
It would seem that since a higher pressure may be generated by the bullets heavier weight that a
Larger safety margin would be needed to vent pressure as the conical passes to the barrel?
I really haven't clue as to the difference a heavier conical produces.
It's just a question on my mind since I only shoot balls in .36 and .44 and the small contact surface of a ball is so small. I understand the small ring of lead is the contact surface.
Just wondering weight vs pressure might require a different ,or wider gap?
Thanks for helping me understand this!

 

[45 Dragoon]

noelf2,
The clearance is measured "as fired". Hammer down, cylinder locked, pulling back on the cylinder. I set them at .002".

ZVP, the clearance isn't for safety, it's for efficiency. The revolver will be more efficient with a close bbl/cyl clearance. The pressures a cap gun sees (without any obstructions) are low and the clearance won't make a difference between safe and unsafe.

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

 

[44 Dave]

Has any one mentioned "arbor damage" ? I acquired an open top that had been fired quite a bit with excessive b/c gap, it has a deep flame cut in the arbor.

 

[noelf2]

45 Dragoon, so with hammer at full cock, there should be no visible b/c gap?

 

[45 Dragoon]

No,
The hand will push the cyl forward to meet the barrel each time you cycle it.! This is how the face of the cylinder "self cleans" and also why it's a "clearance" and not a "gap".

Pull the cylinder back all the way and measure with a feeler gauge.

Also, the tighter the clearance, the less room the cylinder has to hammer away on the two assemblies.

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

 

[noelf2]

Well then I'm pretty sure I have excessive b/c gap on my 1860 Uberti. There's a slight gap still when the hammer is at full cock. When I check the way you described, there is a significant gap. This gun hasn't been shot much, so, it must have been manufactured that way. I'm at a loss, even given the explanations above, to understand how a short arbor and excessive b/c gap can be fixed by messing with the gap left in the barrel assembly because of a short arbor. The wedge fits where it fits, and seems it will still fit where it fits no matter what you do to correct an arbor that doesn't bottom out in the barrel assembly unless you can somehow lengthen the arbor and adjust the location of the wedge slot.

 

[Thompsongunner]

noelf2, what you would do is where the barrel and frame mate. You will pull the two pins out and lap the surfaces until you get your cyl/barrel gap. drill the end of the arbor and tap it for a set screw so the wedge will have a bearing surface. If need be add washers to the arbor hole to give the arbor something solid to seat against. now , this is for ubertis. Piettas you will have to take metal off the arbor to close and overly large cyl/barrel gap.

Hope this helps some.
Gunner

 

[45 Dragoon]

Thompsogunner, very nice!!! (I'm impressed!!)

noelf2, what happens when you drive the wedge in as far as it will go? Does it close the clearance up? Lock up the cylinder?
Depending on the severity of the clearance, you may not have to lap the barrel lug (as Thompsogunner suggests) . It all depends on how much out of spec that relationship is. Thompsogunner's suggestion is correct if the cylinder is way out of spec (too short) which is how you end up with a too much (long) frame situation.

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

 

[Steve's 44cal]

Save yourself the trouble rest your mind and send it to Mike he has been doing this for years and knows just what to do with it and has the proper tools to do so

 

[noelf2]

^^^ Yeah I've resolved to doing that very thing. I plan to keep this gun, so, the other improvements will be good as well. One coming your way soon 45 Dragoon!

 

[45 Dragoon]

Awesome!
Thank you sir!

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks