Chamber mouth to barrel ratios -- cap and ball guns

[Oregon Bill]

Doesn't take a genius to figure out that the chamber diamter has to be at least as big as the barrel groove diamter to provide power and accuracy in a cap and ball revolver, but I have heard that even the latest Piettas get this wrong. Anybody put a micrometer on their sixguns lately? How about those of you with recently purchased Ubertis?
Trying to decide whether to pay for Uberits over Piettas, at least if I go with Colt 1861 Navies instead of 1858 Remington Armies.

[Lars]

Last I knew, everyone but Ruger got it all wrong. The three I have initially had chamber IDa about 10+ thous (yes, ten!!) smaller than groove to groove on barrels. Big improvement when the chambers were reamed out to a few thous over groove to groove of barrels.

I would advise presuming that you will need to get the chambers reamed to get really good performance.

Lars

[Quick Fire]

Lars, I have 4 51navy's made by Pietta. I have not checked any measurement on any of them but all shoot really well. Not bragging but I rarely miss with any of them at matches that I attend. My point is that for most CAS matches The guns don't have to be perfect to hit large steel plates at 7 paces.

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[Major 2]

Here is a link to another thread on this subject ... http://www.cascity.com/forumhall/index.php/topic,6512.0.html

[44caliberkid]

I agree with Lars, all the Italian companies have the chamber mouth too small, but I have two newer Piettas, one a .36 and the other a .44, that shoot excellent, espescially the .36, so I wouldn't worry about it.  The Ubertis will be wrong too.  The chamber mouths on Italian cartridge guns (1873's) are wrong too.  That's why they make chamber mouth reamers.  Rugers are not exempt from this, as many of their cartridge guns (Blackhawks, Vaqueros)  are made with improper diameter chamber mouths.
  With cap 'n ball, a slightly smaller chamber mouth is OK, because you want to cut a little lead ring, to ensure you are getting a good chamber seal, to prevent chain firing.  Additionally, make certain to use pure lead balls or conicals, and the soft lead will "upset" upon firing and expand sufficiently to fill the rifling.
  If you look at original cartridge guns , you will find great variations in chamber mouth and barrel groove diameters from gun to gun, even from the same manufacturer, but ammunition of the period was made with soft, pure lead bullets, that upset under pressure to cover the sins of poor manufacturing tolerances.
   The chamber dimension problem has been more apparent in recent history, when shooters started using hardcast bullets to cut down on leading when using smokeless powder.  The hard alloys don't upset. Another reason to avoid the new fangled heathen powder.
   To summarize, don't spend the extra $100 for a Uberti, they aren't any better in regard to chamber tolerances, and use pure lead for your balls/conicals.

[44caliberkid]

R.C. John, I also have chamfered mouths on some of my C&B pistols, and yes, either method works fine.
I also did not mean to be picking on Rugers, as many revolvers, S&W's and Taurus's, et al, have chamber mouth dimensions bored too small from the factory.

[Lars]

It may well be that the differences in chamber vs groove-to-groove diameters have gotten closer on modern replica C&Bs in recent years. Before I hade the chamber ID on my enlarged to a few thousands of inch over the groove-to-groove diameter of the barrels, they would shoot no better than 6-8 inch groups at 25 yards, no matter what I did. After reaming they would shoot sub 3,0 inch groups for ALL 6 chambers.

The above noted difference in group size is behind the once common reports of 44 C&Bs "shooting better" with R&D 45 Colt conversion cylinders than with their C&B cylinders.

In addition to the smaller groups, the sound of the revolvers changed for a really hollow boom to a very solid sound and there was lots less powder fouling, both the very appearant result of much better combustion of BP thanks to the balls fitting properly.

Ruger Old Armies, at least the ones I know the information about, all have chambers slightly larger in diameter than the groove-to-groove diameter of the barrels.

Lars