Cap and Ball Revolver Dimensions

[Gtek]

I have been collecting these revolvers for several years and have had an understanding of lock up and turned cylinders on the SA's for several decades, Blackhawks were in the house I grew up in and they have multiplied in mine. Now I am getting really serious about making some smoke with these things. There are many videos and articles on how to load, how to shoot, etc. but none I have found on dimension issues of cylinder to bore. I understand the shaving the lead ring and all, but the .001"-.002" over in my head causes distress when I mic, pin, slug and feeler gauge these things out. The .006" on gap, shimming/bushing arbor, fitting barrel is work but capable. The question I cannot get out of my head is how much accuracy and velocity (performance) is lost pushing a .446"-.447" ball into a .452"-.465" grooved barrel. I have a pair of matching 2nd Gen NMA's and a pair of consecutive Pietta 58's that if I used a reamer and took cylinders to .4531" followed by a light polish to <.454" and using a .457" ball, this would land me in the 1-2 over groove thing. OCD? Waste of time, shoot and enjoy as is? Or after correcting all front end dimensions and slicking up timing, correct cylinder dimensions and have me some sweet revolvers to play with? Comments?
Thanks,
Lar---

[Outpost75]

Fit-up of accurate cap & ball revolver should be same as for cartridge. Cylinder throat should not be smaller than barrel groove diameter, and should ideally be not more than about 0.003" over unless 11 degree forcing cone is cut. Back in the day when we fit Colt Python barrels to S&W revolvers for PPC work forcing cone was recut to 6 degrees to provide easy transition of .360" .38 Special wadcutters from huge S&W cylinder throats into the tight .354 Colt barrels and that worked fine.

My Ruger Old Army has .4525" cylinder throats which result in tight fit and short cylindrical bearing surface on a soft 1:40 tin-lead .457 ball when chambered. Barrel groove diameter is same as my Blackhawk .45 Colt, .4505". Ruger Cap & Ball cylinders as factory fitted all have 0.006" cylinder gap to prevent cylinder bind with black powder. Walt Kirst Konversion .45 ACP cylinder has 0.003" cylinder gap, which is fine, because that one never sees black powder. Accuracy is stellar. Forcing cone was recut and lapped to 11 degrees using the Brownell's kit. With target loads, 1:40 .457 roundball and 25 grains Swiss with Cream O Wheat fill, Crisco over ball, get six shots into one hole at 25 yards Ransom Rest. With heavy hunting loads Lee 250 grain R.E.A.L. cast 1:40, SPG lube, 30 grs. 3Fg get 4-5" at 50 yards off Ransom Rest. Good .45 ACP factory jacketed wadcutters in the Kirst cylinder will stay under 3" at 50 yards.

[Gtek]

Yep, kind of confirms thoughts in my mind. The two pair (NMA's/58's) I can work into good numbers. The 61' lands unbelievably .0005" over groove and the ASM NMA is .465" over a .446" cylinder, found new barrel that is .454" and should work with massaged cylinder and Ruger balls.

[Tar Heel]

These guns with pure lead balls work just fine with dimensions as sold. One thing you can do is lightly chamfer the cylinder mouths so as to swage the bullet into the chamber rather than shave it into the chamber. Here is a shot of 36 rounds from an Uberti 1860 Army where I smoothed up the action and chamfered the chamber mouths and broke the sharp edges on the forcing cone. Shots were offhand at 25 yards, 30gr Pyrodex-P, with a RB atop a Homemade lubricated wad. These guns will shoot.

174986 174987 174988

[Nobade]

The surprising thing is that they do actually work. I suppose it is from the hopefully pure lead balls slugging up to fill the rifling. But from my own experimenting, reaming the cylinder up so it is bigger than the barrel's groove diameter, just like you would want a cartridge revolver to be, will give better accuracy and also allow you to use somewhat harder balls to good effect.

-Nobade

[Nobade]

Tar Heel beat me to it! He posted while I was writing.

-Nobade

[Gtek]

Have been doing some serious reading/looking on these platforms and absorbing as much as possible. The chamfer job seems to be one that really helped with also slightly increasing bearing area. That is some fine shooting there, hard to argue with those results. Might require just getting plain silly with it and turn it into project, across Chrony through before and after modifications and documenting results for possible +/- outcome.

[rodwha]

I'd certainly love to see testing done.

Fly reamed my chambers to 0.449" and chamfered them on my Pietta Remington NMA. I'm not sure if it made a difference or not. But then I'm no pistolero either.

[Outpost75]

Great responses all around MSGT Patrick Felker is smiling in Vallhalla...

[Tar Heel]

The surprising thing is that they do actually work.

I know.....right? Like JEEZ! Large...then shaved small....then WHAM...large....small....paper!

[curator]

As Tarheel points out, a cap & ball revolver can shoot quite decently even if chambers are under bore size. With some experimenting you can find a good load. A pure lead ball will obturate some when it hits the rifling, and a wad under the ball will help seal powder gas behind it. Having the chambers correctly sized to .002-3 over groove diameter allows the gun to shoot accurately with just about any load, full power to light target level. A larger ball will also center itself more concentrically through the forcing cone and into the bore allowing for much better long range accuracy. My first replica C&B revolver was a Pietta kit from Dixie Gun about 30 years ago, It had .444 to.446" diameter chambers (all different) and a .451 groove diameter barrel. It would shoot nice round 4" six shot groups from the bench at 50 feet but was not even on a 30X36 target at 50 yards. Reaming the chambers to a uniform .4525 and cutting a 11 degree forcing cone made a HUGE difference. I load .457 diameter balls, FFFg Goex and enough filler, (COW) felt wads, or powder to be sure the ball is flush with the cylinder face with some light compression. No soda can is safe at 50 yards if I can find something the rest the gun on.

[Outpost75]

^^^^^^What he said!!!

Exactly my experience with the Ruger Old Army!