Pietta 1858; barrel and cylinder dimensions issue

[Onty]

Gearing up gradually for my first 36 C&B revolver. Hopefully, in six months I will get Pietta 1858, Target, stainless, 6.5" barrel. So, I started looking for a bullet mold. Suddenly, I realized that something doesn't add up; barrel bore should be .375", but round balls on the market are also .375". If we want to press ball into cylinder, chamber bore has to be somewhat smaller, like .004*.005" for a nice, tight fit. Well, from what I know about lead bullets in revolver, rule of thumb is that bullet coming out from cylinder should be at least the same dia as barrel groove dia, or larger, preferably .001-.002".

Then I started searching about dimensions of barrel and cylinder chamber on Pietta 36 revolvers, and found these two interesting threads:

Tweaking a New Pietta 1851 36 Navy https://www.thehighroad.org/index.php?threads/tweaking-a-new-pietta-1851-36-navy.771583/

pietta 1858 .36 cyl./bore size question

"...If you want a truly accurate Cap & Ball Revolver you are supposed to by the "Shooter Model" that is made with the correct chamber diameter... If your bore/groove diameter is .360/.375, the correct chamber diameter is .376-.378". Reaming the chambers to this diameter (assuming this could be done correctly) and using .380 diameter round balls will give better accuracy with all loads..."

https://www.muzzleloadingforum.com/threads/pietta-1858-36-cyl-bore-size-question.99340/

To make story short, looks like that cylinder chambers' dias in 36 revolvers have, at least, strange dimensions, that are opposite from "conventional wisdom". BTW, both threads are from 2015, so things could get changed in last 7 years.

So, what is your experience and opinion about all this, especially about late Pietta cal. 36 models? Should cylinder chambers be something like .376-.377", and lead balls ,380"?

 

[hawg]

They can be quite accurate the way they are. The soft lead will obturate to fill the bore. I don't know why the Italians make them that way.

 

[Onty]

Looks like Pietta makes cylinder bores .368". On thread https://www.thehighroad.org/index.p...how-it-compares-with-multigroove-ones.912960/ , post #33, there is a design of a bullet that will fit .368" cylinder chambers, and because of hollow base, it should expand and grab rifling in .372-.375" diameter barrels. If some of you have cal. 36 revolver with different cylinder bores, please let me know so I can adjust diameters for those revolvers.

 

[derek45]

I use .380" cast soft lead in my Pietta London Navy 1851

I use .454" balls in my 1860 Army and Remington new model army( pietta's)





I want to see lead rings when I seat bullets

 

[Mizar]

Welcome to the wonderful world of undersized chambers... As one of the Pietta guys explained some time ago (forgot which one exactly, because there are too many of them) it was their way of dealing with excessive fouling, which is a problem especially with new shooters, who don't know how to properly maintain and shoot a black powder revolver. Lots of old BP shooters fall into that category, BTW - you are simply running an undersized projectile thru that barrel, while the grooves are accumulating BP fouling, which can become excessive and raise pressure levels.
I tend to differ from the "bumping up" in size theory, because there is not much resistance or pressure for a round ball, let alone a solid bullet, to obturate (increase it's diameter) in the larger barrel - I still wait for a concrete evidence for that phenomenon, not just theories. But, as Hawg pointed out, revolvers with undersized chambers can be quite accurate, so if this is your primary concern, don't sweat too much about it. Just put a filler, or wad under the ball, or that expanding base bullet with expensive molds you shared. But if you want your gun to be historically accurate as it can be, then ream your chambers to match the groove diameter, or slightly over - that was the way the original guns were build. And lastly - Pedersoli 1858, Pietta and Uberti target models, and even Ruger Old Army (not a 1858 clone, but lookalike) are all build with chambers matching the groove diameter of the barrel - this is something to think of.

 

[hawg]

Yeah, they bump up. I've recovered a lot of fired balls and they all have strong rifling marks.

 

[Mizar]

Yeah, they bump up. I've recovered a lot of fired balls and they all have strong rifling marks.

On the balls I recovered there are burrs on the edges of the engraved rifling - those burrs can only form if there is space. Rifling marks tell you almost nothing, unless you can measure the depth of them and compare it with a slugged ball - those chambers are undersized, but not THAT undersized so the projectile cannot engage the rifling.

 

[Jackrabbit1957]

It's an interesting debate and I see some parallels here. My Ferguson rifle is a .650 bore but if you shoot bore sized balls accuracy falls way off. I shoot a .614 ball and it works very well. When you recover the balls shot through a pistol do you see little wing like thingies sticking out of the grooves? This is what happens when you shoot bore size balls through the Ferg.

 

[Mizar]

Those "wings", which I call "burrs", can form only if there is space between the projectile and the barrel - it happens even with bore sized projectiles, as they get squeezed from the rifling and cannot fill the grooves 100%. This is why I'm skeptic about that "bumping" in size theory - I want measurements and not guessings. Soft lead ball can increase slightly it's diameter from pressure and rifling resistance, but not that much.

 

[Onty]

From https://www.muzzleloadingforum.com/threads/pietta-1858-36-cyl-bore-size-question.99340/ , post # 4:

"Land to land in the bore should be about .360 (thus 36 caliber) and the groove to groove (presuming 2 grooves are exactly 180 degrees opposite) would be .370 to .372 on average."

In that respect, when .375" ball is squeezed into .368" cylinder bore, it will still engage with barrel rifling, without obturation.

I do not have the spec for early C&B revolvers in .44 caliber, but, according to SAAMI spec for 45 Colt, barrel land is .442" dia (barrel groove is .450" dia). Could be that early specs called .44" for land dia, and that is the reason why those revolvers are identified as .44 caliber.

 

[woodnbow]

Yeah, they bump up. I've recovered a lot of fired balls and they all have strong rifling marks.

Same here but I always have a card or wad of some sort under the ball. I made up a bunch of @TheOutlawKid wads, ( paper towels soaked with beeswax lube and 1/2 inch wads cut from it) if I played cowboy games it’s probably what I’d be using.

 

[paul harm]

Back when I shot in the 1970s all we did was buy a gun and shoot it. I didn't know anyone who mic'd a barrel or cylinder. The Lyman booklet that came with my NMA said to use a 451 RB. I shot many a 98 and the occasional 99 or 100. I sold all of them and then got back into shooting BP pistols so I now have five NMAs and haven't mic'd anything - just shoot em and have fun. They seem to shoot quite accurate just the way they are.

 

[hawg]

I never mic'd mine either. I think most people that do that have to wring every iota of accuracy they can out of a gun. They use a two hand hold and probably shoot off of a bench or some kind of brace. I don't shoot paper. I use a one hand unsupported hold and as long as I can hit Coke cans at 25 yards more often than not I'm happy.

 

[woodnbow]

I’ve never shot competition with these guns and back in the 60’s didn’t mike the guns either. .454 balls and bullets were all I ran. I do like to wring them out so sometime in the 70’s when I had more time and money I began to mike these and the cartridge guns at the same time n pursuit of accuracy. Some days I plink at steel, some days I’m trying to hit bowling pins at a hundred yards, another day I might bang away at an old oil drum up on the canyon wall, and others I’m on a bench rest trying to make tiny groups. I have to say, I enjoy it all.

 

[paul harm]

Shooting pistol on the Nation range is off hand, or one hand for those who don't know. I use to start getting a little serious about it a month or so before we'd go and shoot my Daisy one pump air pistol down the basement everyday. At 24 feet my groups would go from 3 or 4 inches to a 1/2" at the end of the month. At 25 yards you'd need to make one ragged hole to win in the Master class. Were I'd fail was the 50 yard line. That 50 yard line would show all your mistakes or faults. But it was still fun trying. If I got in the 80s/100 I was happy.