Arbor Shim for Dragoon

[Norton Commando]

Well I was cleaning my new Dragoon this afternoon and discovered that the cylinder-to-barrel-gap was too tight < 0.006”. Upon closer inspection, I discovered that the arbor does not bottom out in its corresponding hole in the barrel.

So, no shooting for me this weekend until I get the gap sorted out.

Questions please:

1) What should the cylinder-to-barrel-gap be on a Dragoon, I assume 0.006” to 0.010”?

2) What is the best shim material to use in the bottom of the barrel hole to adjust the cylinder-to-barrel-gap?

Thanks a bunch!

Jason

 

[Smokin'Joe]

Regarding the arbor shim material I use brass shim stock. Cut it for a snug fit and it will stay in place without any adhesive.

 

[72coupe]

Norton there are threads about how to properly finish the arbor hole in the barrel of Uberti's. Search those out they are interesting reads.

 

[Hellgate]

All of my Colts have a gap of .007" with no fouling problems so you are not that far off. .006" is probably fine. I think .01 is too wide but that's just my opinion.

 

[Norton Commando]

Makos reports a recommended cylinder gap of 0.008" to 0.010" for Colt cap and ball revolvers. I guess this gap range would apply to the Dragoon, too? For shim material, I'm thinking about carbon steel. My concern about using aluminum or other less noble material is galvanic corrosion; perhaps I'm overly concerned here?

For a temporary "fix" I carefully adjusted the thickness of two steel washers, one smaller in OD than the other one. I installed the smaller one in the barrel bore first, followed by the larger OD washer. The thinking here about the two different diameters is that the washers would better "fill" the bottom of the tappered hole in the barrel.

The frame lug and arbor now make contact at the same time. However, my cylinder gap is about 0.006", which is probably too tight, so I may have to take some material off the barrel cone.

I'm open to suggestions.

Thanks,

Jason

 

[Smokin'Joe]

Do yourself a favor and Do Not remove any metal from the barrel. Shoot the gun before you do anything drastic. .006" is not too tight. Some shooters go as tight as .002".

Check out: http://www.thehighroad.org/showthread.php?t=587863

BTW I would not be concerned about Galvanic action causing corrosion. Most of these guns have steel and brass in constant contact without any ill effects.

 

[Caliper_Mi]

I will second 0.006 not being too tight. I'll get numbers from my revolvers, but there is barely light between the cylinder and forcing cone on one.
What problems do you expect from a tighter gap? Seems like tighter would give a cleaner gun and a bit more velocity.

 

[Norton Commando]

BluEyes,

Yes, a few thousandths tighter gap should provide more pressure and therefore provide slightly more bullet velocity. However, the velocity increase is probably immeasurable.

My concern is that too tight a clearance may cause binding. Moreover, I’m going by what Makos has documented in previous posts as the optimum cylinder gap for Colt cap and ball revolvers, which is 0.008” to 0.010”. So assuming this information is correct for a Dragoon, then it follows that my measured 0.006” gap is too tight.

Notwithstanding the above, I may shoot it the way it is and see how it behaves.

Jason

 

[col.lemat]

Try it as is first then adjust if needed. You cant put it back on once it off. It can be done but it's beyond most peoples capibility

 

[makos_goods]

Norton,
Shoot it the way it is, at least for now. And I'll give you an interim solution. If you are a target shooter and not cooking off more than about 50 rounds a session you could probably live with .006" though you may want to clean the barrel face, arbor at the cylinder gap and the cylinder face maybe every 4 cylinder loads. That .006" is set by the depth you insert your wedge since you have already told us your arbor doesn't bottom out. You could temporarily set the wedge not as deep as long as the spring hook just catches or goes beyond the opposite side of the frame.

Since you are citing my previous posts I am assuming you have referred to Pettifogger's articles about correcting the lengths of Uberti arbors? If you have, then have you determined more or less how much space there is that creates the problem between your arbor and the bottom of the hole? It's shown on the third page of his third installment:

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

Several of my CAS buddies use spring washers at the bottom of the hole. There seems to be a consensus that a 1.1mm thick (.043") spriing washer seems to fit most Ubertis.

Here's where we talk about them:

http://www.cascity.com/forumhall/index.php/topic,35698.msg459992.html#msg459992

Here's a link to a great online source for hardware just like this. This is a direct link to the washer:

http://www.mcmaster.com/#91169a170/=e2qagy

If I had to choose a gap for all of my percussion pistols I would chose .009". Remember you don't have the gas ring at the front of the cylinder of a more modern design to set your end shake and with that your cylinder gap. I respect Hellgate's experience because he shoots C&B revolvers in CAS like I do where a fouled pistol can cost you a stage, but I have chosen the more conservative path since it seems that was the maker's original intent. So I will always offer .008"-.010" as being a reliable and very usable cylinder gap for a C&B revolver without a gas ring.

Regards,
Mako

 

[Norton Commando]

Thanks for all the replies/suggestions. It seems strange to have to work on a brand new gun, but such is the routine in the pattern black powder gun world.

I actually have a generous 0.006" cylinder gap with washers installed in the arbor hole, so I plan to shoot it like this. My range is shut down due to the nearby fires, so I'll have to travel a bit to find a safe shooting space.

Jason

 

[Caliper_Mi]

Yes, I agree the increase in velocity is likely negligible, that was more tongue in cheek...

I checked my pistols and couldn't fit a .002 feeler between any. These are a Pietta Remington, bought new, Uberti Dragoon, bought new and made with the right length arbor and an Uberti 1860, made in the 70's. The 1860 needs the arbor shimmed but shoots good groups anyways. My Rem will start to drag on the cylinder axis before there is any problem rubbing the cylinder to the barrel.

 

[Norton Commando]

I checked my pistols and couldn't fit a .002 feeler between any.

Wow, that makes my 0.006" gap seem like the Grand Canyon!

Thanks for the follow-up there BluEyes.

 

[72coupe]

The more you shoot it the larger the gap will get. Eventually you will be wanting to close the gap.

 

[madcratebuilder]

The old Colt spec for barrel gap is .008. Shoot the gun and see if the gap changes at all. .006 well be fine, I've run as tight as .004 without any problems with build up causing drag. Barrel gap has less effect on velocity with black powder revolvers because of the lower operating pressures compared to smokeless powders.

I make my lug shims from brass stock, I thread the ID so I can attach a threaded rod to remove if I want.

 

[Norton Commando]

Hey madcrate - great idea about threading the ID of the shim, thanks!