Cylinder chamber diameter vs groove diameter and accuracy

There have been a couple of other threads that have touched on this topic recently, but thought I would give this its own thread.

In an effort to better understand the historical relationship between the cylinder chamber and groove diameters, I measured an original 1858 Remington that I own that happens to be quite a tack driver.
With the right shooter behind it, it has shot groups with 6 shots touching at 25 yards.

Rifling is sharp, but very shallow. Didn’t slug and measure groove diameter, but it is definitely less than what Pietta cuts theirs to (.006” deep) or Uberti’s deeper grooves (.0095”). Bore measures right at .436”. If the rifling is .004/.005” deep as it appears, that puts the groove diameter at .444/.446”. The cylinder chambers diameters all measure.450” (.450” gauge pin drops in, .451” pin barely starts).

Believe this groove to bore diameter relationship is a big part of why the gun is still so accurate after 150 plus birthdays. While I don’t currently have any original Colts to measure, the few I have been involved in measuring all had cylinder chamber bores larger than groove diameters. Coincidence? Maybe. I just find it interesting that some seem to argue that it’s no big deal that Pietta and Uberti cylinder chambers are smaller than groove diameter, plus they know what they are doing.... must be some other reason why it’s so inaccurate...

Just my observation from a very small sample size. Curious if others have taken measurements of originals and what they found?

Racing and Len and Omnivore on the 58 Forum would be the most notable to answer those questions. Racing lives in a country where he can buy only original firearms but no replicas. For a young man he does amazing work. Omnivore does a lot of experimenting on bullets and load development for 58's. Len is another artisan with the 58's. Yolla Bolla Brad is another one who modifies his 58's chambers to match groove diameters. Give 'em a shout they love to help.
DL

.449 right at recommended for 44cal. Does depend on the actual bore max measured. My walker cylinder is bored .451 and that works well for it.
I measured my 36 cal Piettas and they all measured. 374-.376. .375 ball is real easy to ram, too easy for me so I shoot .380 ball.
My Pietta 1858s in the more accurized model will shoot just as good with any of the 8 cylinders I have. Never had any need to even measure them.
I did try to get an answer from Uberti and Pietta about this but the only answer I recieved was, they are just reproductions. Considering only my walker was odd out of the 7 I have it seem it is a sporadic issue.

.449 right at recommended for 44cal. Does depend on the actual bore max measured. My walker cylinder is bored .451 and that works well for it.
I measured my 36 cal Piettas and they all measured. 374-.376. .375 ball is real easy to ram, too easy for me so I shoot .380 ball.
My Pietta 1858s in the more accurized model will shoot just as good with any of the 8 cylinders I have. Never had any need to even measure them.
I did try to get an answer from Uberti and Pietta about this but the only answer I recieved was, they are just reproductions. Considering only my walker was odd out of the 7 I have it seem it is a sporadic issue. Even my Rogers and Spencer measures correct and its over 40 years old.

I've still got to do a lot of shooting to determine the best accuracy load for each of my C&B revolvers. But even so I am thinking I will have the cylinders reamed to around .379.

I had been conversing with a C&B 'smith about doing that before I started the chamber/bore thread here. (He holds the same opinion as you Snuffy!) Unfortunately I lost all the emails and his information. Does anyone know a C&B workman who reams cylinders?

atllaw said:

I've still got to do a lot of shooting to determine the best accuracy load for each of my C&B revolvers. But even so I am thinking I will have the cylinders reamed to around .379.

I had been conversing with a C&B 'smith about doing that before I started the chamber/bore thread here. (He holds the same opinion as you Snuffy!) Unfortunately I lost all the emails and his information. Does anyone know a C&B workman who reams cylinders?

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Was it the Colt 60 or 58 Rem originals with gain twist?

SDSmlf said:

There have been a couple of other threads that have touched on this topic recently, but thought I would give this its own thread.

In an effort to better understand the historical relationship between the cylinder chamber and groove diameters, I measured an original 1858 Remington that I own that happens to be quite a tack driver. View attachment 15969
With the right shooter behind it, it has shot groups with 6 shots touching at 25 yards.

Rifling is sharp, but very shallow. Didn’t slug and measure groove diameter, but it is definitely less than what Pietta cuts theirs to (.006” deep) or Uberti’s deeper grooves (.0095”). Bore measures right at .436”. If the rifling is .004/.005” deep as it appears, that puts the groove diameter at .444/.446”. The cylinder chambers diameters all measure.450” (.450” gauge pin drops in, .451” pin barely starts).

Believe this groove to bore diameter relationship is a big part of why the gun is still so accurate after 150 plus birthdays. While I don’t currently have any original Colts to measure, the few I have been involved in measuring all had cylinder chamber bores larger than groove diameters. Coincidence? Maybe. I just find it interesting that some seem to argue that it’s no big deal that Pietta and Uberti cylinder chambers are smaller than groove diameter, plus they know what they are doing.... must be some other reason why it’s so inaccurate...

Just my observation from a very small sample size. Curious if others have taken measurements of originals and what they found?

Click to expand...

I ream my chamber mouths to groove or no more than .001 over groove diameter and they have all shot well. Also with ball shooters it is best to keep the forcing cone as short as possible in my opinion. I found this out by firelapping a 58 Rem which demonstrated a real dive in accuracy after the lap job. I checked the cone with a ball and could see that the lapping had extended the cone depth. I set the barrel back and recut the forcing cone which restored the accuracy.
If you check any of the reproductions you will likely find two things.
1. The chamber mouths will not all be the same diameter.
2. They are seldom perfectly round.
Carefully reaming the chamber mouths will correct both of these deficiencies. The best way I have found to ream them is to remove the barrel and make a tight fitting spud that is put in place of the barrel through the frame which holds the reamer squarely and snugly keeping chamber mouths co-axil with the bore. It is pretty close to line boring the chambers with the barrel although not quite as exacting because you are not boring new chamber holes with a locked in cylinder blank that has been super fitted to the frame bolt.

M. De Land said:

Was it the Colt 60 or 58 Rem originals with gain twist?

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No, it was 3 - 36 Cal revolvers and a (Uberti) Richard's conversion.

atllaw said:

No, it was 3 - 36 Cal revolvers and a (Uberti) Richard's conversion.

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I'm pretty sure a least the 1860 Colt had a gain twist from the factory.

Started this thread because I was curious about other’s experiences matching cylinder bore diameters to groove diameter.

Most recent Pietta 1858s and 1860s I have obtained have .438 bores, with groove diameters at .450”. Multiple cylinders I have measured were in the .444” range, +/-.001. Reaming them to .451-.452” in general, cut group size by more than half. At 25 yards, went from 6-7”, usually caused by one or two unexplained flyers, down to 2-3” or better consistently. Same powder and charge. Same wad and lube. Same caps. Same shooter. Only difference is reamed cylinder chambers.

Curious, at least to me, that m this is not a major point of discussion amount others.

I agree 100%. This has always been the method of accuracy in revolvers at large and no reason it does not apply to C&B revolvers.

I personally believe that three things set modern replica's down a notch or two when your best accuracy is desired with these revolvers.

First is exactly this descusion on matching cylinder mouth diameter down into the cylinder a ball diameter in depth ( no reason to bore them any deeper ). This allow's the ball the oppertunity to swage down to completely fill "immediately" the WHOLE groove of the barrel ... therefore making gas cutting a thing of the past.

Second is the hammer spring strength. These replica's have a pretty lite spring to begin with and folks gravitate towards even liter springs. This makes an uneven ignition and allows pressure to escape in varying degree's from the nipple which produces uneven ignition and pressure inside the chamber.

Thirdly is the nipple itself. They need to be just right in outer dimension so that the cap set's perfectly down on the nipple face which should be nice and flat and square to allow the cap the opportunity to set down completely on the face of the nipple and yet be tight enough to not fall off under recoil ... having a small inner hole to help prevent excessive gas escape from ignition.

These things will prevent a few problems associated with malfunction of the revolver AND way better accuracy.

Again just another muttering from the peanut gallery.

I don’t have an accurate way to measure cylinder diameter (could push a ball back out I suppose and use my calipers) but accepted that Pietta’s have ~.446” chambers, but my 2013 NMA has .452” grooves and .442” lands.

A fellow interested in my custom bullets made a deal in which he teamed my chambers to .449” for some projectiles. Honestly I can’t tell a difference, but then it’s still not groove diameter and so I’ve been considering a hand reamer to get them closer and I’d stop right at the bolt notches.

My shooting was all done at 15 yds with a Weaver-like hold and my NMA groups (with a ball or my 170 and 195 grn bullets) ran 3.5-4” whereas my ROA with those projectiles and several more gave me 3-3.5” groups. I’ve wanted these groups at 25 yds so as to feel good about hunting with them.

As an aside I’ve noticed the bottoms of those chambers are rounded and don’t hit the base of the nipples and have wondered, like the ROA, if that can be touched up as well. Not that I’m not satisfied with standard .45 ACP performance but for hunting a little extra can’t hurt, and the price wouldn’t likely be much more if they’re getting reamed anyway.

Oh, and my more accurate load with a service charge in my NMA is 30 grns of 3F Olde E (and T7) that weighs ~33 grns. I started at 25 grns and worked in 5 grn increments as I use an adjustable rifle measure. I have a new one that I’ve scratched in 2.5 grn increments and will eventually retest.

rodwha said:

I don’t have an accurate way to measure cylinder diameter (could push a ball back out I suppose and use my calipers) but accepted that Pietta’s have ~.446” chambers, but my 2013 NMA has .452” grooves and .442” lands.

A fellow interested in my custom bullets made a deal in which he teamed my chambers to .449” for some projectiles. Honestly I can’t tell a difference, but then it’s still not groove diameter and so I’ve been considering a hand reamer to get them closer and I’d stop right at the bolt notches.

My shooting was all done at 15 yds with a Weaver-like hold and my NMA groups (with a ball or my 170 and 195 grn bullets) ran 3.5-4” whereas my ROA with those projectiles and several more gave me 3-3.5” groups. I’ve wanted these groups at 25 yds so as to feel good about hunting with them.

As an aside I’ve noticed the bottoms of those chambers are rounded and don’t hit the base of the nipples and have wondered, like the ROA, if that can be touched up as well. Not that I’m not satisfied with standard .45 ACP performance but for hunting a little extra can’t hurt, and the price wouldn’t likely be much more if they’re getting reamed anyway.

Oh, and my more accurate load with a service charge in my NMA is 30 grns of 3F Olde E (and T7) that weighs ~33 grns. I started at 25 grns and worked in 5 grn increments as I use an adjustable rifle measure. I have a new one that I’ve scratched in 2.5 grn increments and will eventually retest.

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Rodwha, what is your lube procedure and makeup?

I did a test once with my paper cartridges consisting of mandrel wrapped Zig Zag cig papers, 22 grains 3F OE powder, home cast .375 diameter pure soft lead ball's, paper twisted over the top of the ball, dipped in bee wax/Vasoline 50/50 mix down about 1/8th inch below the ball. I shot 50 of these as fast as I could load em and accurately shoot them on a solid rest at 25 yards. All 50 in a 4 inch group with 4 or 5 outside this group ( me ).

I have also repeatedly tested round balls loaded over 22 grains 3F OE powder and ... wait for it ... lubed with plain unsalted Crisco OVER the ball. This has been repeatedly the BEST accuracy load I have ever tested.

I have yet to do the reaming of my cylinder ... but ... remain convinced that with a cylinder diameter of .001 to .002 inch over groove diameter will net the same or better accuracy then the unmentionables get which is 1 to 2 inch at 25 yards. No reason this can not be achieved. Same basic principal's apply.

Keep us posted as to your progress please

bigted said:

Rodwha, what is your lube procedure and makeup?

I did a test once with my paper cartridges consisting of mandrel wrapped Zig Zag cig papers, 22 grains 3F OE powder, home cast .375 diameter pure soft lead ball's, paper twisted over the top of the ball, dipped in bee wax/Vasoline 50/50 mix down about 1/8th inch below the ball. I shot 50 of these as fast as I could load em and accurately shoot them on a solid rest at 25 yards. All 50 in a 4 inch group with 4 or 5 outside this group ( me ).

I have also repeatedly tested round balls loaded over 22 grains 3F OE powder and ... wait for it ... lubed with plain unsalted Crisco OVER the ball. This has been repeatedly the BEST accuracy load I have ever tested.

I have yet to do the reaming of my cylinder ... but ... remain convinced that with a cylinder diameter of .001 to .002 inch over groove diameter will net the same or better accuracy then the unmentionables get which is 1 to 2 inch at 25 yards. No reason this can not be achieved. Same basic principal's apply.

Keep us posted as to your progress please

Click to expand...

I use Gatofeo’s #1 lube either on a felt wad or in the narrow and slightly shallower lube grooves on my bullets (and on the Lee REALs). Just keeps on running. Been meaning to try it on the patches for my rifle too. Grape seed oil doesn’t seem to do a good job but it was the only oil Karmen would let me use (should have seen the berating I got when she caught me looking at her olive oil!).