Undersized chambers in revolvers???

[m-g willy]

I got Flyer from Dixie Gunworks . And while going through it I noticed they gave chamber and barrel groove measurements for their revolvers that show the barrel dia. .010 over chamber dia. on most revolvers!. ,And on a first model dragoon they show .456 groove dia. and a .449 chamber dia..But on the high end (SHOOTERS REVOLVER 1858 FOR $895) they show matching chamber and barrel groove at .456....How much will a lead ball bump up when going from undersize chamber to larger barrel grooves? I have revolvers that are anywhere from chambers .002 larger than barrel grooves to chambers that are .005 smaller than barrel grooves.My most accurate cap and ball revolver is a Uberti 1851 navy with chamber and barrel grooves matching at .379.that will shoot 2" groups at 25 yards (On a good day).I also have 3rd model dragoon with 453 chambers and a .458 barrel that averages 6-8" at 25 yards...So if it's because o f the difference between barrel and groove dia. ..What gives with selling new guns with undersized chambers?

 

[Long Johns Wolf]

It is my understanding that all Italian percussion replicas incl. the 2nd and 3rd gen Colts have chambers' dia thare are less than the rifling groove dia.
Why?
Because they replicated the originals from the 19th century.
Exceptions are the Belgian made Centaures (Colt 1860 pattern) were the rifling groove dia is adjusted to the chamber dia, and ca. 50 % of the Spanish (later) made Remington New Model 1863 Armies.
The rational of the Belgians and later also of Spanish Santa Barbara was that they wanted to make the most accurate percussion revolvers ... which they did.
Long Johns Wolf

 

[Scota4570]

There are several threads on this subject to enjoy. I reamed my Pedersoli to 0.452. The bore is .0450. It now shoots very accurately. Look for revolvers with a 0.450-ish bore. That means that Uberti is out of the running. Uberti is 0.454. To bad they are the best made, but the barrel is screwed up. There is a limit to how much you can ream a cylinder. They get thin. Also 0.457" is the largest non custom ball mold.

My answer to the OP question is, stubbornness and institutional thinking. The is no good reason to insist on making them wrong when you know better. They just don't care enough to make it right.

The CAS guys shoot at a 24" plate at 7-yards. They don't need a barrel to hit it. Casual uninformed shooters don't care. The few percentage who understand this issue are unimportant to the Italian makers.

The Italians only need to make the barrels tighter. That involves simply resharpening the bore setting reamer and rifling broach to the correct size. It would costs them nothing. I get the feeling the Italians are not so much shooters as gun sellers. As sellers they are successful. It is not a problem to them, no need to change.

I sent a courteous detailed email letter to Uberti USA on the subject. I got no response. That says all we need to know.

 

[rodwha]

It is my understanding that all Italian percussion replicas incl. the 2nd and 3rd gen Colts have chambers' dia thare are less than the rifling groove dia.
Why?
Because they replicated the originals from the 19th century.
Exceptions are the Belgian made Centaures (Colt 1860 pattern) were the rifling groove dia is adjusted to the chamber dia, and ca. 50 % of the Spanish (later) made Remington New Model 1863 Armies.
The rational of the Belgians and later also of Spanish Santa Barbara was that they wanted to make the most accurate percussion revolvers ... which they did.
Long Johns Wolf

I can’t say for sure, but it seems I recall the few original cap n ball guns measured by capandball had oversized chambers. No?

 

[arcticap]

Dixie has had those same revolver specifications posted on their website for a long time.
I read them with a huge grain of salt.
They may have had some basis in reality at one time but who knows if they still do.
I doubt that they measure each new batch of revolvers that have passed through their shop since those spec.'s were posted,
so I would consider them to be merely representational.
Each and every gun is unique, and how well each chamber aligns with the forcing cone is going to be different with every gun.
But that is why some people choose to accurize their guns.
Some outfits make higher priced competition models for those who want to spend the extra money.
Perhaps if we knew the manufacturer's wholesale prices for these reproductions not including the cost of shipping and taxes,
then we wouldn't be so critical of their spec's.
If the Ruger Old Army were being made today, it would probably cost more than most are willing to pay.
And there's a reason why Euroarms went out of business too, even though the Rogers & Spencer was a fairly popular model
and known for its accuracy.
The current makers probably don't have a large profit margain per unit.
At least they don't have as much competition as they used to, and can sell more guns worldwide to help keep production & quality reasonably high.
If the prices weren't fair then many folks would stop buying them.

Some folks might say that the diameter of the projectile gets bumped up when it gets blasted out of the chamber.
I suppose that there are ways to collect fired balls and examine whether they are actually being engraved with rifling or not as they pass through the barrel.
I'd guess that they probably are to some degree.
But if not, there are always skirted, heeled or bevel base bullets that may be able to better expand when fired.

 

[rodwha]

Dixie has had those same revolver specifications posted on their website for a long time.
I read them with a huge grain of salt.
They may have had some basis in reality at one time but who knows if they still do.
I doubt that they measure each new batch of revolvers that have passed through their shop since those spec.'s were posted,
so I would consider them to be merely representational.
Each and every gun is unique, and how well each chamber aligns with the forcing cone is going to be different with every gun.
But that is why some people choose to accurize their guns.
Some outfits make higher priced competition models for those who want to spend the extra money.
Perhaps if we knew the manufacturer's wholesale prices for these reproductions not including the cost of shipping and taxes,
then we wouldn't be so critical of their spec's.
If the Ruger Old Army were being made today, it would probably cost more than most are willing to pay.
And there's a reason why Euroarms went out of business too, even though the Rogers & Spencer was a fairly popular model
and known for its accuracy.
The current makers probably don't have a large profit margain per unit.
At least they don't have as much competition as they used to, and can sell more guns worldwide to help keep production & quality reasonably high.
If the prices weren't fair then many folks would stop buying them.

Some folks might say that the diameter of the projectile gets bumped up when it gets blasted out of the chamber.
I suppose that there are ways to collect fired balls and examine whether they are actually being engraved with rifling or not as they pass through the barrel.
I'd guess that they probably are to some degree.
But if not, there are always skirted, heeled or bevel base bullets that may be able to better expand when fired.

They certainly get engraved. Look at the land measurements. Do they always fill in the grooves? Maybe. The Pietta Remington Pocket may not with the dimensions they produce it in.

A question I have is what impact there is on the projectile needing to be obturated. Does it take away from its performance? It seems those who’ve reamed their chambers claim a noticeable difference in accuracy. I suspect obturation takes away a little of the performance. Maybe it’s insignificant. Often a larger ball seems to show an increase in velocity with the same powder charge. Maybe because it fills the grooves better?

I’d certainly prefer better accuracy and better performance if reasonably possible. I keep thinking I’ll buy a hand reamer and open up my Pietta chambers further from 0.499” to 0.451-2”. Not only to potentially improve it but because I share projectiles with my ROA and relieving loading stress sounds good to me as well.

 

[Scota4570]

"A question I have is what impact there is on the projectile needing to be obturated."

Poor accuracy? I guess an example might be of use. The Ubertis I recently examined had 0.448 chambers and a 0.454 bore, .006" undersized. Would you expect good accuracy by shooting a 45 ACP (.451) bullet in a 45-70(.457)? That is the same amount of undersized we are taking as the Uberti 1858.

 

[rodwha]

"A question I have is what impact there is on the projectile needing to be obturated."

Poor accuracy? I guess an example might be of use. The Ubertis I recently examined had 0.448 chambers and a 0.454 bore, .006" undersized. Would you expect good accuracy by shooting a 45 ACP (.451) bullet in a 45-70(.457)? That is the same amount of undersized we are taking as the Uberti 1858.

What I meant by my question is whether or not the act of obturation the projectile would steal energy. In other words would there be a loss of velocity. It seems accuracy is a given.

We certainly modern arms all use lead projectiles that are over groove diameter. There’s clearly a reason, though in some it could well be the use of hardcast projectiles that can’t obturate. But we see the over groove sizing even in soft lead.

And another question would be just how undersized can the projectile be and obturate enough to fill those grooves? Of course this is dependent on the powder and charge but at some point there just won’t be enough.

 

[curator]

There are several advantages in having the chamber diameter being the same size as the barrel's groove diameter or even a few thousandths over. A larger ball will have more surface area in contact with the rifling. If the ball seals the grooves and prevents powder gas from leaking it will be naturally centered in the bore. A smaller diameter ball having less area in contact with the bore can be pushed to one side by high pressure gas finding the least resistance down one or two grooves. I have recovered balls fired from replica C&B revolvers that showed rifling marks on only one side. Those balls were fired into deep snow so were not deformed from impact.

When working as a museum firearms curator, I had the opportunity to measure more than 100 original C&B revolvers from many manufacturers. While some did have chambers slightly smaller than bore (groove) diameter, nearly all had correctly proportioned chamber/barrel diameters. I suspect those with undersized chambers were the result of the manufacturer trying to get longer operating life from well used reamers.

 

[nkbj]

Typical measurements that I've taken on Colt and Remington repro's have been bores smaller than chambers and chambers smaller than grooves. That makes it practical to use a thin skirted hollow base bullet design.

 

[Scota4570]

What I meant by my question is whether or not the act of obturation the projectile would steal energy. In other words would there be a loss of velocity. It seems accuracy is a given.

We certainly modern arms all use lead projectiles that are over groove diameter. There’s clearly a reason, though in some it could well be the use of hard cast projectiles that can’t obturate. But we see the over groove sizing even in soft lead.

And another question would be just how undersized can the projectile be and obturate enough to fill those grooves? Of course this is dependent on the powder and charge but at some point there just won’t be enough.

"would steal energy"? I have no information, if you want more zip shoot Swiss BP.
"It seems accuracy is a given" ... not if the ball is obturating randomly or rattling down the barrel.
"hard cast projectiles that can’t obturate." Modern guns...But, they do obturate. That is key to cast bullet accuracy. Too hard bullets leak gas, gas cut, and lead. To soft and they strip. Just right they obturate a tiny bit to make seal and do not lead. Balancing the charge and powder speed vs the hardness of the alloy is very important to cast bullet accuracy.

Agreed. Using bullets, even hollow base bullets would be helpful. The accuracy would never be as good as it could have been, if the gun was made properly in the first place. Some NMLRA competitions only allow balls, so for my purposes it is irrelevant.

 

[arcticap]

"A question I have is what impact there is on the projectile needing to be obturated."

Poor accuracy? I guess an example might be of use. The Ubertis I recently examined had 0.448 chambers and a 0.454 bore, .006" undersized. Would you expect good accuracy by shooting a 45 ACP (.451) bullet in a 45-70(.457)? That is the same amount of undersized we are taking as the Uberti 1858.

Perhaps those spec.'s were accurate measurements for that specimen.
But in 2016, the MLAIC World Champion for the 1st ever open top World Championship event won it with a stock Uberti 1847 Walker
and I don't believe that he even altered the sights since he had to aim at the bottom of the target.
He answered a question about his gun just past the 2 minute mark of the video.
But if you watch the entire video you'll see how well he shoots with it, even though it's just an informal shooting session with capandball.
Imagine winning a World Championship with an off the shelf Walker, the winning model for the first time event ever.

 

[rodwha]

"would steal energy"? I have no information, if you want more zip shoot Swiss BP.
"It seems accuracy is a given" ... not if the ball is obturating randomly or rattling down the barrel.
"hard cast projectiles that can’t obturate." Modern guns...But, they do obturate. That is key to cast bullet accuracy. Too hard bullets leak gas, gas cut, and lead. To soft and they strip. Just right they obturate a tiny bit to make seal and do not lead. Balancing the charge and powder speed vs the hardness of the alloy is very important to cast bullet accuracy.

Agreed. Using bullets, even hollow base bullets would be helpful. The accuracy would never be as good as it could have been, if the gun was made properly in the first place. Some NMLRA competitions only allow balls, so for my purposes it is irrelevant.

We are not on the same page here. Let me see if I can make it make more sense.

I said:

“What I meant by my question is whether or not the act of obturation the projectile would steal energy. In other words would there be a loss of velocity. It seems accuracy is a given.”

I’m not sure how to make this any more clear. I’m wondering if the act of obturating reduces the pressures/robs the projectile of its velocity to do so. If a gun’s chambers were undersized and shot with X powder charge would reaming the chambers to bore or just over increase the velocity as the pressures are no longer working to obturate the projectile.

Oh, and I use 3F Olde Eynsford and Triple 7 so there’s plenty of zip as they are comparable to Swiss.

As to “accuracy being a given” I had earlier stated this:

“It seems those who’ve reamed their chambers claim a noticeable difference in accuracy.”

It seems a given that reaming the chambers improves accuracy, therefor it’s a given.

If a projectile is groove diameter or larger how is it going to obturate to fill a gap that isn’t present?

 

[M. De Land]

It should be mentioned what exactly happens in a cap-n-ball revolver regarding the balls travel from cylinder mouth to forcing cone then bore. The ball is actually introduced into the forcing cone by a plug of yet to be burned powder which does not actually burn until the ball or bullet has transitioned the forcing cone and is well on it's way up bore.
An undersized balls only mechanism to bump up (expand) is inertia were as a ball of groove diameter meets resistance as soon as it inters the back of the forcing cone.
The as yet un-burned powder in the chamber acts as a gas seal on an under sized ball until it is consumed and then hot gas escapes around the base of the ball or bullet, in the grooves, causing erosion (leading) and loss of velocity.
The other thing is an under sized ball does not evenly engrave the rifling as would a groove diameter ball.
What about the wad as a seal if used? Well an over sized wad is actually an undersized bore seal as it bends around the lower half of the ball when the top of the powder column at the base of the ball finally burns. I believe the wads benefit is actually more of a bore sweep to clear fouling than it is gas seal , especially under a ball.

 

[William P Sepessy]

Dixie has had those same revolver specifications posted on their website for a long time.
I read them with a huge grain of salt.
They may have had some basis in reality at one time but who knows if they still do.
I doubt that they measure each new batch of revolvers that have passed through their shop since those spec.'s were posted,
so I would consider them to be merely representational.
Each and every gun is unique, and how well each chamber aligns with the forcing cone is going to be different with every gun.
But that is why some people choose to accurize their guns.
Some outfits make higher priced competition models for those who want to spend the extra money.
Perhaps if we knew the manufacturer's wholesale prices for these reproductions not including the cost of shipping and taxes,
then we wouldn't be so critical of their spec's.
If the Ruger Old Army were being made today, it would probably cost more than most are willing to pay.
And there's a reason why Euroarms went out of business too, even though the Rogers & Spencer was a fairly popular model
and known for its accuracy.
The current makers probably don't have a large profit margain per unit.
At least they don't have as much competition as they used to, and can sell more guns worldwide to help keep production & quality reasonably high.
If the prices weren't fair then many folks would stop buying them.

Some folks might say that the diameter of the projectile gets bumped up when it gets blasted out of the chamber.
I suppose that there are ways to collect fired balls and examine whether they are actually being engraved with rifling or not as they pass through the barrel.
I'd guess that they probably are to some degree.
But if not, there are always skirted, heeled or bevel base bullets that may be able to better expand when fired.

I have purchased 10 Uberti cap & ball pistols since 2014. FWIW, the chamber mouth dimensions in both .36 & .44 have been very close to what is listed in Dixie's catalog. Again, these were all Ubertis'. Maybe I'm just lucky.

 

[nkbj]

For .44's I'm kinda partial to the idea of mass producing barrel liners of the rifling dimensions best suited to the undersized chambers. The .36's usually have plenty of extra wall thickness in the cylinders for reaming but the .44's... the .44's bug me.

 

[Scota4570]

" For .44's I'm kinda partial to the idea of mass producing barrel liners of the rifling dimensions best suited to the undersized chambers. The .36's usually have plenty of extra wall thickness in the cylinders for reaming but the .44's... the .44's bug me."

For and 1858, A modern barrel of 45 ACP dimensions would be correct. It would be round but that would be fine with me. This would also work great for a messed up Ruger Old Army. They used a 45 LC Blackhawk barrel.

 

[rodwha]

For .44's I'm kinda partial to the idea of mass producing barrel liners of the rifling dimensions best suited to the undersized chambers. The .36's usually have plenty of extra wall thickness in the cylinders for reaming but the .44's... the .44's bug me.

Yes. Wall thickness looks a bit thin at 0.449” as it is.

 

[zimmerstutzen]

I have had several cap and ball revolvers over the years, some very accurate as made and some sloppy and poor accuracy. Folks make the automatic assumption that a chamber size less than bore groove is a loss of accuracy. However, there is some obturation or bumping up from the impact of ignition. There is also an effect of pushing the ball into rifling. Where the ball is compressed by the rifling, does it swell sufficiently along side into the grooves to fill them? It is not just a simple geometry calculation. It is difficult to measure just by slugging a ball into the rifling, for depending on what forces are used to push the ball, it will swell abnormally. The lands pressing into the circumference of the where the ball rides the bore take up some of the chamber diameter. The lead compressed/displaced by the lands must go some where. I suppose, in all directions, both along the land and into the groove. This would be especially so where a sightly larger ball is used. A bigger ring is shaved off the ball diameter, creating a wider bearing surface along the lands when the ball is pushed into the rifling.

 

[drobs]

I seem to recall a gentleman on another board pressing a ball into a chamber so it shaved a ring of lead. Then tapping it out of the chamber from a nipple hole and using the same ball to slug the bore. I believe his results were just fine.

Seems like a lot of work to me but I'm not a competition / bullseye shooter.