how to best slug a revolver barrel?

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hrt4me

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What is your preferred method of slugging a revolver barrel to determine its ideal bullet diameter?
I am interested in your various tips and techniques...
Also, how would you measure the chamber diameters in the cylinder?
 

hawkeye2

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Take a round ball of larger diameter that the bore and pound it into the muzzle using a rawhide or wooden mallet. Push it through the bore with a dowel and measure. I measure the chambers using a dial caliper but you can slug them too. Drive a ball in, run a screw into the ball and pull with pliers. In case you don't have a ball larger than the bore take a smaller one, lay it on a hard surface and strike it a couple of times with a hammer to increase its diameter.

If you don't have any measuring tools slug the bore (as above). Take that ball and try it in the chambers. If it goes into a chamber without shaving then that chamber is larger that the bore (ideal situation) and if it shaves lead then it's smaller than bore diameter.
 
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Bad Karma

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What is your preferred method of slugging a revolver barrel to determine its ideal bullet diameter?
I am interested in your various tips and techniques...
Also, how would you measure the chamber diameters in the cylinder?
If a Colt, dismount the barrel, put a .490 ball into the forcing cone and drive it in with a 3/8” brass rod. I do this With the barrel held vertically muzzle resting on a leather covered bench. if a top framed revolver I clamp the barrel in my barrel vice with a bit of rosin on the leather covered jaws.
 

ZUG

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I run a clean patch first then I run a patch with oil down both barrel & cylinder then an oversized ball. Remove it then measure it. The first two steps is something I do to make me happy :ghostly:
 

rafterob

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Not sure why the need to slug the barrel. The ball is formed into the barrel after being shot from the cylinder. Some cylinders are actually undersized of the bore and you will see posts of the owners reaming them out to be slightly larger to ensure a tight fit of the ball in the barrel. It is the cylinder that determines the size of the ball.
 

Pietro

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FWIW, in over 50 years, I've never measured the diameters of either the ball or chambers of my C&B revolvers.

IMO, the thin lead ring shaved off the ball during seating it the chamber is a good thing, ensuring a good seal at the chamber mouth.

All of my C&B revolver's chambers are slightly smaller that the bore, and accuracy doesn't seem to suffer, most likely due to a slight obturation of the ball when fired - but, what do I know ?
 

rodwha

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FWIW, in over 50 years, I've never measured the diameters of either the ball or chambers of my C&B revolvers.

IMO, the thin lead ring shaved off the ball during seating it the chamber is a good thing, ensuring a good seal at the chamber mouth.

All of my C&B revolver's chambers are slightly smaller that the bore, and accuracy doesn't seem to suffer, most likely due to a slight obturation of the ball when fired - but, what do I know ?
I would guess there’s a very good reason why match shooters don’t use undersized chambers.
 

rodwha

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I use a .457” ball lubed with Ballistol. I’ve also removed the nipple and forced the ball back out to measure the chamber.
 

rodwha

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Not sure why the need to slug the barrel. The ball is formed into the barrel after being shot from the cylinder. Some cylinders are actually undersized of the bore and you will see posts of the owners reaming them out to be slightly larger to ensure a tight fit of the ball in the barrel. It is the cylinder that determines the size of the ball.
How would you know if you’d want/need to team your chambers if you have measured the bore?
 

nkbj

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Ever see a revolver with chambers diameter the same as the bore of the barrel? Not the groove diameter but the bore? Changing the ball diameter won't help a bit.
 

M. De Land

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What is your preferred method of slugging a revolver barrel to determine its ideal bullet diameter?
I am interested in your various tips and techniques...
Also, how would you measure the chamber diameters in the cylinder?
I lube the bore well with a oiled patch on a cleaning rod then remove the cylinder and secure barrel with padded vice jaws. I then drive an over size soft lead slug through the bore from muzzle to breech and mic the land diameter on the slug which will be the grooves of the barrel. I start the slug with a brass drift and once in the barrel drive it on through with a dowel rod. To get bore diameter and chamber mouth the best way is to use plug gauges or a split ball gauge and then cross mic . Caliper jaws are imprecise for measuring ID of barrel or chambers and quiet often you will find chamber mouths out of round and different diameters from each other.
 

necchi

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What is your preferred method of slugging a revolver barrel to determine its ideal bullet diameter?
I am interested in your various tips and techniques...
Also, how would you measure the chamber diameters in the cylinder?
Cerrosafe. Melt's with boiling water,,has simple instructions and never wears out,, it can be used over and over and over.

The stuff is available from several suppliers.
But as others have said,, the "chamber size" determines the size delivered to the forcing cone that passes the ball to the bore.
So you see, "bore" diameter should be a known as you measure it. But it's the cylinder that determines what ball size should be used.
Some use 451,or 454, or 457,, and there are other increments for different calibers.
But it's what is delivered to the barrel that matters,, chamber size and barrel work together
 

M. De Land

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Cerrosafe. Melt's with boiling water,,has simple instructions and never wears out,, it can be used over and over and over.

The stuff is available from several suppliers.
But as others have said,, the "chamber size" determines the size delivered to the forcing cone that passes the ball to the bore.
So you see, "bore" diameter should be a known as you measure it. But it's the cylinder that determines what ball size should be used.
Some use 451,or 454, or 457,, and there are other increments for different calibers.
But it's what is delivered to the barrel that matters,, chamber size and barrel work together
Actually the barrel groove diameter should determine the ball diameter and the chamber mouths and forcing cone adjusted to it and not more than .001 over. This is true of bullet or ball. I believe forcing cone depth for round ball use should be approximately half a ball diameter for best accuracy.
I both have and use cerrosafe casting metal but it is much more useful for barrel chamber casting than barrel lands and grooves although it can be used for that as well. The reason is because it expands over time. You have about a 30 to 60 minute window to make your measurement before it will begin to expand and some times it doesn't want to leave the lands and grooves of a barrel after it cools.
A pure lead slug is better in my opinion because it remains stable to it's bumped up size as it exits and will represent the end of the barrel it is pushed out of.
Chambers and their mouths almost always need to be uniformed to each other because they are gang reamed and each reamer has a sharpening tolerance deemed exceptable to the manufactures standard. This can very and often does by quite a bit. The mouths are also often out of round by a bit as well when mic'ed by a split ball gauge.
Forcing cones often need uniforming as well and they are best cut from the muzzle with a two bore bushing set up to keep the drive rod and thus cutting head centered.
These are all things done to match pistols to make them shoot to full potential. Factory guns would be far more expensive if this were done by the manufacturer.
Another thing one will almost universally find when using pin or slug gauges is differing bore (land) diameters along your barrels length . Careful hand lapping will remove this both in land or groove.
 
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M. De Land

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Cerrosafe shrinks a bit as it cools so it can release from a casting but I find it often sticks in a barrels lands and grooves and has to be melted out. I'm not quite sure why this is so but have experienced it often. It works fine in barrel chambers though. It may be because most barrel chambers have a bit of taper and a barrel bore is cylindrical. It may also be from lead contamination because it often is melted in the same pouring spouts when used.
 

necchi

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M. De Land; Your right, with both your posts. I hope others will read and understand what you have shared.
When it comes to the Cerrosafe stuff, as I recommended, I hope people read and follow directions for using the alloy, and/or watch the many you tube videos of it's use. It has non-typical behavior for a metal that most are used too, because it's:
" a fusible alloy with a low melting point. It is a non-eutectic mixture consisting of 42.5% bismuth, 37.7% lead, 11.3% tin, and 8.5% cadmium that melts between 158 °F (70 °C) and 190 °F (88 °C). It is useful for making reference castings whose dimensions can be correlated to those of the mold or other template due to its well-known thermal expansion properties during cooling. The alloy contracts during the first 30 minutes, allowing easy removal from a mold, then expands during the next 30 minutes to return to the exact original size. It then continues expanding at a known rate for 200 hours, allowing conversion of measurements of the casting back to those of the mold."

Trouble is,, one has to grasp the concept of alloy,,
 

nkbj

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Actually the barrel groove diameter should determine the ball diameter and the chamber mouths and forcing cone adjusted to it and not more than .001 over. This is true of bullet or ball. I believe forcing cone depth for round ball use should be approximately half a ball diameter for best accuracy.
I both have and use cerrosafe casting metal but it is much more useful for barrel chamber casting than barrel lands and grooves although it can be used for that as well. The reason is because it expands over time. You have about a 30 to 60 minute window to make your measurement before it will begin to expand and some times it doesn't want to leave the lands and grooves of a barrel after it cools.
A pure lead slug is better in my opinion because it remains stable to it's bumped up size as it exits and will represent the end of the barrel it is pushed out of.
Chambers and their mouths almost always need to be uniformed to each other because they are gang reamed and each reamer has a sharpening tolerance deemed exceptable to the manufactures standard. This can very and often does by quite a bit. The mouths are also often out of round by a bit as well when mic'ed by a split ball gauge.
Forcing cones often need uniforming as well and they are best cut from the muzzle with a two bore bushing set up to keep the drive rod and thus cutting head centered.
These are all things done to match pistols to make them shoot to full potential. Factory guns would be far more expensive if this were done by the manufacturer.
Another thing one will almost universally find when using pin or slug gauges is differing bore (land) diameters along your barrels length . Careful hand lapping will remove this both in land or groove.

For quite a while now I've been suspecting that the best cure for Pietta's 1858's isn't reaming the chambers but rather replacing the barrel with rifling of the right diameter, geometry and twist. For the price of a barrel blank made to order and a group buy on a smith reworking half a dozen revolvers...
Half a dozen pistoleros might get to have the revolvers of their dreams.
 

hawkeye2

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There are a number of smiths out there who regularly rebarrel Pietta and other revolvers with barrels made to their specs. At least one has Bobby Hoyt rifle the blanks. I expect they all ream the chambers as part of the job too. No need to do a group buy.
 

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