Is it recommended to bore out cylinder to barrel diameter on Italian replica revolvers?

[Majorsideburns]

After reading online that chamber dimensions differ from the bore on these replica revolvers, I measured my cylinder chambers on my Pietta replica Colt and Remington and sure enough my cylinder chambers are smaller than the bore. On my 1860 the cylinder chambers measure between .448" and .450" but the bore grooves of the barrel measure .458". Is it worth having a gunsmith ream these out to match the bore diameter? Has anyone here done this and experienced noticeable gains in accuracy? And why don't they come properly sized from the factory?

 

[Bad Karma]

Wow! .458” is very large. I would remeasure it to make sure it’s right. If you reamed chambers .001” over groove diameter you will need balls or bullets over .460” or more. (I use .465” balls in the Pietta Shooter Model which is bored .456” from the factory. Some of my other guns were bored to match by Charlie Hahn.)

 

[jdesro]

After reading online that chamber dimensions differ from the bore on these replica revolvers, I measured my cylinder chambers on my Pietta replica Colt and Remington and sure enough my cylinder chambers are smaller than the bore. On my 1860 the cylinder chambers measure between .448" and .450" but the bore grooves of the barrel measure .458". Is it worth having a gunsmith ream these out to match the bore diameter? Has anyone here done this and experienced noticeable gains in accuracy? And why don't they come properly sized from the factory?

How are they in regards to accuracy the way they are?

 

[Majorsideburns]

How are they in regards to accuracy the way they are?

Well it's tough to answer that truthfully because I'm no crack shot. I mostly shoot offhand and just plink at large targets 7 or 10 yards away. I think the last time I shot for groups on paper from a bench was a few years ago with my 1851 .44 Pietta and I was getting about 8" groups at 25 yards. I do remember having worse accuracy with the highest charges and the best accuracy was with the lower starting charges which surprised me because I assumed the higher max charges would force the lead to deform and fit tight in the rifling. I'll have to really try sighting them carefully from a bench to get a truer idea of their capability.

 

[Bad Karma]

Well it's tough to answer that truthfully because I'm no crack shot. I mostly shoot offhand and just plink at large targets 7 or 10 yards away. I think the last time I shot for groups on paper from a bench was a few years ago with my 1851 .44 Pietta and I was getting about 8" groups at 25 yards. I do remember having worse accuracy with the highest charges and the best accuracy was with the lower starting charges which surprised me because I assumed the higher max charges would force the lead to deform and fit tight in the rifling. I'll have to really try sighting them carefully from a bench to get a truer idea of their capability.

Even a 15 grain charge is quite a boot in the rear. The point of chambers sized at least groove diameter is that the transition from chamber through the forcing cone and into the bore is less upsetting and allows a tighter gas seal, less lead fouling, etc. I have always noted an increase in accuracy when the chamber and bore are sized in harmony. Sometimes just because the factory reamers were cutting oval AND undersized chambers… it doesn’t hurt to clean them up. And if I couldn’t get better then 8” at 25 yards I would be looking for solutions. Maybe it’s more trigger time, maybe it’s the gun, maybe it’s a combination.

 

[jdesro]

Well it's tough to answer that truthfully because I'm no crack shot. I mostly shoot offhand and just plink at large targets 7 or 10 yards away. I think the last time I shot for groups on paper from a bench was a few years ago with my 1851 .44 Pietta and I was getting about 8" groups at 25 yards. I do remember having worse accuracy with the highest charges and the best accuracy was with the lower starting charges which surprised me because I assumed the higher max charges would force the lead to deform and fit tight in the rifling. I'll have to really try sighting them carefully from a bench to get a truer idea of their capability.

That's kind of the direction I was going with my question.

We firearms enthusiasts tend to get a kick out of modifying things - sometimes just for the sake of modifying things, whether they need them or not.

I'd say you should really get a good idea of how the revolver shoots, and factor that in to what you are using the revolver for.

If 8" groups at 25 yards is really the best it will do, then it probably could use a little work - if you are going to be shooting it at 25 yards a lot.

But if most of your shooting is plinking at close targets, 8" at 25 yards works out to about 2.75" or so at 7 yards. Certainly good enough to hit tin cans at that distance.

So I guess what I'm getting at is that I wonder if the expense and effort of reaming the cylinder is worth it. Don't forget, if you ream out the chambers you are now going to have to source larger projectiles, which means, if you cast your own, finding a mold that will work with your cylinder. If you do not cast your own, finding the right size pre-made balls might be troublesome.

 

[SDSmlf]

After reading online that chamber dimensions differ from the bore on these replica revolvers, I measured my cylinder chambers on my Pietta replica Colt and Remington and sure enough my cylinder chambers are smaller than the bore. On my 1860 the cylinder chambers measure between .448" and .450" but the bore grooves of the barrel measure .458". Is it worth having a gunsmith ream these out to match the bore diameter? Has anyone here done this and experienced noticeable gains in accuracy? And why don't they come properly sized from the factory?

Curious to hear how you are taking the dimensions?

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.

 

[Nobade]

I have consistently found better accuracy by making the chambers as big as the barrel's groove diameter and radiusing the mouth. Also a good polished forcing cone is a big improvement as well.

 

[Notchy Bob]

After reading online that chamber dimensions differ from the bore on these replica revolvers, I measured my cylinder chambers on my Pietta replica Colt and Remington and sure enough my cylinder chambers are smaller than the bore. On my 1860 the cylinder chambers measure between .448" and .450" but the bore grooves of the barrel measure .458". Is it worth having a gunsmith ream these out to match the bore diameter? Has anyone here done this and experienced noticeable gains in accuracy? And why don't they come properly sized from the factory?

That is a pretty big difference.

It is very difficult to get an accurate inside measurement with calipers. Even with precision calipers, if they are even slightly canted or off center, you will get an undersized measure. If the caliper jaws are flat, you’ll be measuring a “chord” across the edge of the circle, even if the caliper is dead center and not canted. Before even considering reaming the chambers, you need to know for certain what you are dealing with. A professional gunsmith or machinist may have plug gauges that will yield an accurate measure, or you can remove the nipples and load some slightly oversized pure lead balls (obviously, with no powder), and then gently drive them back out with a brass rod inserted through the nipple seat. Mike these slugs to get an accurate measure of each chamber. You may want to slug the barrel, too, although if there is an odd number of grooves it may be tough to get a really accurate measurement.

Another thing to consider is the thickness of the chamber walls in your cylinder, both the outside wall thickness and the webs between chambers. You will want to consider this seriously, as it appears from post #4 that you sort of want to shoot higher charges.

If, after all, you do get the chambers reamed and need oversized balls, Buffalo Arms sells Pedersoli round ball moulds in a variety of nonstandard sizes in the .460” to .470” range.

I would strongly recommend that you make a realistic determination of how you expect to use your revolver (plinking at cans, hunting, fierce bullseye competition, etc.), get accurate measurements of your chambers and bore, and determine the safety limitations of modifying the revolver before removing any metal.

Good luck, and be safe!

Notchy Bob

 

[Bad Karma]

I have consistently found better accuracy by making the chambers as big as the barrel's groove diameter and radiusing the mouth. Also a good polished forcing cone is a big improvement as well.

Are you recutting the forcing cone? Some guns may require this. But most probably not. On the advice of trusted smiths I check by dropping one of the bullet or balls into the forcing cone and if roughly half of the projectile is outside the forcing cone, it’s probably just fine, assuming the machining is relatively clean.

 

[Lippy984]

It made a big difference in my Italian clones

 

[M. De Land]

After reading online that chamber dimensions differ from the bore on these replica revolvers, I measured my cylinder chambers on my Pietta replica Colt and Remington and sure enough my cylinder chambers are smaller than the bore. On my 1860 the cylinder chambers measure between .448" and .450" but the bore grooves of the barrel measure .458". Is it worth having a gunsmith ream these out to match the bore diameter? Has anyone here done this and experienced noticeable gains in accuracy? And why don't they come properly sized from the factory?

My feeling is they will shoot balls fine with under sized chamber mouths if they are all the same diameter and round which they seldom are from the factory but if one wants to also shoot conical bullets then the chamber mouths need to be opened up to groove diameter.
I haven't noticed any down side to ball shooting when chambers are opened up if ball diameter is increased accordingly. This may very likely have as much to do with the uniforming of the chamber mouths then the increasing of the diameter, in ball shooting.
One of my pet peeves about shaving lead rings is they are only meaningful if chamber alignment allows for a full circumference trim ring. Partials are not sealing the chamber mouth and this is where an over sized lubed felt wad seated with the loading lever ahead of the ball or bullet does the sealing.
This is where the tapered chambers can be of use when shooting conicals as the bullet base can be swage fit to seal off against the taper with the lube ring ahead of it.
Remember only to open the mouths of the chambers particularly in rebated cylinders just deep enough to allow seating under the barrel loading lever. If one has to use a loading lever extension on the barrel ram than it will likely be bent at some point.

 

[M. De Land]

My feeling is they will shoot balls fine with under sized chamber mouths if they are all the same diameter and round which they seldom are from the factory but if one wants to also shoot conical bullets then the chamber mouths need to be opened up to groove diameter.
I haven't noticed any down side to ball shooting when chambers are opened up if ball diameter is increased accordingly. This may very likely have as much to do with the uniforming of the chamber mouths then the increasing of the diameter, in ball shooting.
One of my pet peaves about shaving lead rings is they are only meaningful if chamber alignment allows for a full circumference trim ring. Partials are not sealing the chamber mouth and this is where an over sized lubed felt wad seated with the loading lever ahead of the ball or bullet does the sealing.
This is where the tapered chambers can be of use when shooting conicals as the bullet base can be swage fit to seal off against the taper with the lube ring ahead of it.
Remember only to open the mouths of the chambers particularly in rebated cylinders just deep enough to allow seating under the barrel loading lever. If one has to use a loading lever extension on the barrel ram than it will likely be bent at some point.

Groove diameter in odd numbered rifling can only accurately be measured with a driven barrel slug or cerosafe cast and then measured with a tri-mic or Powley gauge which is what I use.
Virtually all chamber mouths I have measured are not uniform to each other or even perfectly round from the factory. I always check them with my set of plug gauges along with the bore (land) diameter of the barrel and then a driven slug or cerosafe cast down bore to check groove diameter.
I also lap out all tight spots found in the bore with a plug gauge which I have no idea if beneficial other than to eliminate bore leading in some cases. If the bore doesn't lead I have my doubts as to it's usefulness but it always makes be feel better to lap to a level bore at least.
I do like to lap in a bit of taper choke in rifle barrels but for hand gun a level bore is plenty good enough.

 

[M. De Land]

After reading online that chamber dimensions differ from the bore on these replica revolvers, I measured my cylinder chambers on my Pietta replica Colt and Remington and sure enough my cylinder chambers are smaller than the bore. On my 1860 the cylinder chambers measure between .448" and .450" but the bore grooves of the barrel measure .458". Is it worth having a gunsmith ream these out to match the bore diameter? Has anyone here done this and experienced noticeable gains in accuracy? And why don't they come properly sized from the factory?

Here are some pictures of me opening up the chambers on an 1860 reproduction in need of chamber mouth uniforming.
The chamber centers are found with a plug gauge on the x-y axis milling table set up on the drill press. Once center is found the plug gauge is replaced by the reamer and a depth plug is dropped in so both depth and reaming is uniform. We know were on center when fresh steel is reamed all the way around the chamber mouth when only adding a thousands or two to diameter.This method relies on bolt notch index from the factory as all were lining up with is the factory center of each chamber. It seems to work quite well but is not as accurate as frame line reaming.
This leaves a small 45 degree angle shoulder in the base of the chamber mouth to seat a conical base against or lube wad and has no effect on ball shooting.
If it were a solid frame gun I would do the job through the frame hole with a reaming jig so as to line bore it with the bolt notch index.

 

[Nobade]

Are you recutting the forcing cone? Some guns may require this. But most probably not. On the advice of trusted smiths I check by dropping one of the bullet or balls into the forcing cone and if roughly half of the projectile is outside the forcing cone, it’s probably just fine, assuming the machining is relatively clean.

Only if it needs it. A few do. But usually it just needs to be lapped smooth and polished.

 

[M. De Land]

Are you recutting the forcing cone? Some guns may require this. But most probably not. On the advice of trusted smiths I check by dropping one of the bullet or balls into the forcing cone and if roughly half of the projectile is outside the forcing cone, it’s probably just fine, assuming the machining is relatively clean.

I almost always cut the muzzle crown cleanly and very often touch up the forcing cone if eroded, cut rough or cock-eyed.

 

[M. De Land]

Only if it needs it. A few do. But usually it just needs to be lapped smooth and polished.

Brownell's sells a very good kit for cutting both muzzle crowns and forcing cones that I use regularly on both modern and percussion guns. I some times have to turn a new brass bushing to fit the bore diameter of the gun I'm working over but I have never seen a more accurate cutting and lapping tool for muzzle crown or forcing cone work.

 

[Bad Karma]

Brownell's sells a very good kit for cutting both muzzle crowns and forcing cones that I use regularly on both modern and percussion guns. I some times have to turn a new brass bushing to fit the bore diameter of the gun I'm working over but I have never seen a more accurate cutting and lapping tool for muzzle crown or forcing cone work.

4D Rentals will rent the tools for folks who may only do it once or twice…

 

[M. De Land]

Brownell's sells a very good kit for cutting both muzzle crowns and forcing cones that I use regularly on both modern and percussion guns. I some times have to turn a new brass bushing to fit the bore diameter of the gun I'm working over but I have never seen a more accurate cutting and lapping tool for muzzle crown or forcing cone work.

Here are a couple of photos of what the tools look like, what a new cut and lapped cone should look like and how a ball should fit the cone.
It's a T handle, bushing centered hand cutting tool. The tool shown is for the cone. The crown tool has a single cutting edge of 45 degrees but is used on the same T handle/bushing set up.
It is important to use some lube and to start easy so as not to get a chatter going as they are difficult to stop and remove once they get going and usually need to be lapped out.
I've learned much of this stuff the hard way so listen and save your self some grief !
The brass angular tool above the cutter in the third photo is a lapping slug used after the cone is cut with the tool.
A properly fit and lapped cone goes a long way in helping correct chamber misalignment inaccuracy but of course dead nuts alignment is always preferred as it minimizes ball or bullet distortion and out of axis projectile which is more important with bullets than balls .

 

[BillinOregon]

Nice shop, Mr. De Land. Thanks for the tutorial images.