Oversized Revolver Chambers

[Sven205]

That’s a larger cylinder bore diameter than I have found on unmolested Ubertis, and about correct in my opinion for their .458” barrel groove diameter.

This Uberti has been worked over by Mr. Hahn. I recommend his work if youre looking into boring a cylinder or anything similar.

The Pietta is stock.

 

[SDSmlf]

What year is yours? Mine is a 2013 Sheriff’s model, and I slugged mine and found it to be .4525” X .442” and with a 1:16” twist (really thought it would comein 1:30”).

I’ve got more than nine Pietta NMAs, a mix of Sheriff and standard models of various manufacturing dates, and when I measured them I remember them being pretty consistent, .438 +/-.001” bores, and .450 +/-.001” groove diameter. I used gauge pins to check the bore diameter, then slugged the barrel and measured the grooves on vision system. Find it somewhat difficult to get repeatable dimensions measuring slugs from these and other barrels with odd numbers of grooves/lands with mics or calipers. Opposite every land is a groove and you have to be very careful to get constant and accurate dimensions, at least in my opinion.

 

[SDSmlf]

This Uberti has been worked over by Mr. Hahn. I recommend his work if youre looking into boring a cylinder or anything similar.

The Pietta is stock.

Appreciate the recommendation. I’ve already modified the cylinders myself.

 

[rodwha]

I’ve got more than nine Pietta NMAs, a mix of Sheriff and standard models of various manufacturing dates, and when I measured them I remember them being pretty consistent, .438 +/-.001” bores, and .450 +/-.001” groove diameter. I used gauge pins to check the bore diameter, then slugged the barrel and measured the grooves on vision system. Find it somewhat difficult to get repeatable dimensions measuring slugs from these and other barrels with odd numbers of grooves/lands with mics or calipers. Opposite every land is a groove and you have to be very careful to get constant and accurate dimensions, at least in my opinion.

Hmmm. Mine has 6. Are these all older models and/or non standard models? Thought it would come with the typical slow twist but found it fast at ~1:16”. Are yours slow twist?

 

[SDSmlf]

Hmmm. Mine has 6. Are these all older models and/or non standard models? Thought it would come with the typical slow twist but found it fast at ~1:16”. Are yours slow twist?

Checked two of mine, one a standard NMA, one a Sheriff model, DOM 2008 (CC) and 2011 (CH), would call them older, as that is what I call my original 1858. Both Piettas I looked at had 7 grooves, just as I remembered. I’ve never seen a Pietta NMA with 6 grooves, but appears they made yours, so there must be more out there.

I don’t remember checking the twist, but most pistols I have checked seemed to have a much faster twist than any roundball rifle.

I have found for best accuracy, that having the cylinder chambers diameters .001”/.002” larger than the barrel groove diameter, with .452” diameter working best with my Pietta NMAs, at least in my opinion.

 

[nkbj]

Seems the Pietta chambers provide a great opportunity for experimentation.
Reaming to .451" diameter by about 0.4" or so in depth with a very generous taper between the two diameters would be just about right. That way I could size bullets from all those .45 pistol and revolver molds to .450" and .457 round ball would work just fine also.

 

[rodwha]

I’d take it to at least groove diameter. For me that’s .453”, which makes the shared bullets for my Ruger that need to be just a little larger, and so reduces the stresses of loading on the Remington, and supposedly increases the accuracy.

And I’d take that down to 1.1” which is a few hairs from the beginning of the stops. I wouldn’t want the base of my bullets sized down to .446” or whatever Pietta chambers tend to be. That would probably kill my first driving band. Here’s an interesting observation:



As you can see, for all practical purposes, the NMA and ROA cylinders are the same length, yet it holds maybe 6-7 more grains of powder. The Ruger being beefier of course and not dealing with issues of thin bolt stops. And we know that Clements and a few others will clean those up and gain 5-10 more grains of powder volume, thereby giving it Dragoon capacity.

what time does huntington bank close

santander banking

I’d love to see my NMA’s (and ROA) cleaned up some down in there, not to gain more powder as my accurate hunting charge is plenty. What I would like to gain is bullet length being that they share this bullet and pigs are mostly what I have in mind.

 

[M. De Land]

What year is yours? Mine is a 2013 Sheriff’s model, and I slugged mine and found it to be .4525” X .442” and with a 1:16” twist (really thought it would comein 1:30”).

What year is yours? Mine is a 2013 Sheriff’s model, and I slugged mine and found it to be .4525” X .442” and with a 1:16” twist (really thought it would comein 1:30”).

Whats the land count in your barrel ? If odd it's real hard to get an accurate read on a slug without a try mic or Powlly gauge. My 1995 1860 Pietta Colt has seven and is not a gain. I've hand lapped it and you cannot lead slug lap a gain twist.
Also the term bore seems to get used often as not when one means groove diameter. The bore diameter is the land diameter.

 

[nkbj]

Pietta does have different styles of rifling in 1858's.
Didn't see that until recently. The faster twist rifling I see now has wider grooves and looks like modern guns as opposed to the previously supplied style.
Are all the new Pietta 1858 barrels like that?

 

[rodwha]

Whats the land count in your barrel ? If odd it's real hard to get an accurate read on a slug without a try mic or Powlly gauge. My 1995 1860 Pietta Colt has seven and is not a gain. I've hand lapped it and you cannot lead slug lap a gain twist.
Also the term bore seems to get used often as not when one means groove diameter. The bore diameter is the land diameter.

6 lands and grooves:



Thanks for pointing out “bore.” I thought bore had been calculated by land diameter but changed to groove diameter, how the .44 became the .45.

 

[rodwha]

Mine has thin grooves.

 

[M. De Land]

Mine has thin grooves.

I believe the mix up comes from how barrels were manufactured then. The were drilled and reamed thus forming the bore which is the bead for the cutting head. Any tight or loose spots in the bore is reflected into the groove as the rifling head responds to the diameter change.

 

[M. De Land]

Not only do the chambers often come of different diameters they also often are not perfectly round. A worn and resharpened reamer put back into service is what I believe to be the cause. Chamber reamers have a plus and minus tolerance and when they are ground back while sharpening this makes them cut increasingly smaller diameter chambers until they are out of spec. My guess is the chambers are gang reamed simultaneously {six different reamers going at the same time} which is why they are often of differing diameters.

 

[nkbj]

Well hot dog.
Got a .446 sizer coming for all those WC, RN and SWC molds.
And the new to me sheriff's model 1858 has the fast twist barrel and .447 chambers. Triple Seven and .446 bullets are gonna be some fun.

 

[wb78963]

In the armory are six Pietta Colt open top type revolvers in .44 caliber. Each has had hundred or more shots using .451" hand cast ball, lube wad, and remington #10 cap on Slixshot cones.
On loading there is a small shaving of lead and so far no chain fire occurrences.
I have used a few .454" Hornady swaged balls and saw no apparent improvement at CAS ranges. They were a bit harder to load that was all.
I have not bothered to measure the diameter of the chambers.
it ain't broke. It don't need fixin', just shootin' that is all
HOWEVER
YMMV
Load 'em heavy boys
they air a'comin'
Bunk

 

[nkbj]

Not only do the chambers often come of different diameters they also often are not perfectly round. A worn and resharpened reamer put back into service is what I believe to be the cause. Chamber reamers have a plus and minus tolerance and when they are ground back while sharpening this makes them cut increasingly smaller diameter chambers until they are out of spec. My guess is the chambers are gang reamed simultaneously {six different reamers going at the same time} which is why they are often of differing diameters.

I've seen stepped chambers, different depth chambers, tapered chambers, out of round chambers and varying diameters.
About the only thing not run into yet is seriously choked.

 

[Kansas Jake]

In line with what wb78963 posted, I've had good experience with Pietta manufactured revolvers using .451s. I have a Rogers & Spencer Euroarms that needs .454 at least for a seal. It is in rough shape so that may have something to do with it also.

 

[M. De Land]

Mine has thin grooves.

Have you ever run a plug gauge down bore to see how consistent your bore diameter is? Looking at your muzzle bore it looks like it might could benifit from a good lap job and deeper chamfer at the crown.

 

[rodwha]

I have not (don’t own them). I’ve wondered the same thing about that crown, and hadn’t even realized just how rough the bore does look until I took that pic. It made me consider running some sort of compound through it a little to see if I can smooth it up a bit after I empty it.

I don’t recall now, but someone had tried to convince me the crown wasn’t so important on a pistol. I don’t see the logic, but I’m not knowledgeable on things like this.

 

[M. De Land]

I have not (don’t own them). I’ve wondered the same thing about that crown, and hadn’t even realized just how rough the bore does look until I took that pic. It made me consider running some sort of compound through it a little to see if I can smooth it up a bit after I empty it.

I don’t recall now, but someone had tried to convince me the crown wasn’t so important on a pistol. I don’t see the logic, but I’m not knowledgeable on things like this.

Good uniform bores and crowns are always a positive accuracy enhancement it's just hard to notice with hand guns unless sand bags or a machine rest is used so it can show up. I've found that bore smoothness is not nearly as important as bore uniformity and a plug gauge or two will show this very readily.
I have this old rolling block I picked up last year in .43 Spanish. The bore was pitted and rough as a cob with a tight spot just in back of the front sight. I wanted to experiment with my notion that a rough bore is just as accurate as a smooth one if it does not deform the bullet and will spin it properly for it's length. I lapped the manure out of it until I got rid of the tight spot , cut a new crown in the lathe and the ole girl shoots like a house of fire pits and all.
I used it at a gong match clearing all ten chickens at 50 yards and then later on knocked down four rams at 200 meters with it.