'Sizing' a gun barrel info needed

[Patriot]

When I go to purchase cast bullets I find that there are a number of
sizes in the same caliber offered. Can anyone tell me the best way
to 'size' a barrel so that I can get on with ordering the correct bullets?

For instance, in the case of a .32 caliber bullet I can order .311", .312", .313", .314"
and some, if not all, recommend 'sizing' the barrel in order to get the correct size.

I also see where equivalent bullets in lead and jacketed are different for the
most part with lead being typically .001" over the jacketed dimension. Is this
true for all lead/jacketed bullet combinations for the same caliber?

I bought jacketed .32 H&R bullets, both Sierra and Hornady and they are both
.312" (can't get them any other size, I think) so would that make the lead
bullet I am seeking .313"?

I think that I would rather 'size' the barrel to know what the sizes of the two
different firearms I have that are chambered in this caliber but unfortunately I
I think that I might have neither the tools and I definitely do not have the
knowledge about how to do this the 'right way'. The caliper didn't seem to
cut it when I tried it.

TBP

 

[GTOShootr]

Just google "slugging a barrel"

http://www.surplusrifle.com/reloading/slug/index.asp

 

[Cross-X]

The procedure is called slugging a barrel. Believe it or not, to do it, the author suggests you obtain a lead fishing sinker, and use it to take a measurement of your barrel's diameter.

Here is a link how to do it -- http://www.surplusrifle.com/reloading/slug/index.asp

 

[EddieCoyle]

TBP,

If you're loading for a revolver, it's not so much the barrel that you need to size, it's the bore coming out of the chambers. Matching the bullet size to bore size is the most important thing you can do for accuracy. The barrel has a forcing cone and it will take care of itself. The best way to measure the bore diameter of the individual chambers within a revolver cylinder is with a set of plug (a.k.a. pin) gages. Like these.

They're pretty easy to use - just keep dropping them in one at a time, going up in size until one doesn't fit. Read the number off the last one that fit and you've got your bore (and bullet) size.

If you're loading for an autoloader or rifle, then get a soft piece of lead slightly larger in diameter than the barrel, and drive it through the barrel with a wooden dowel. Afterward, simply measure the diameter of the slug - including the protrusions caused by the rifling grooves. This is a lot easier if there are an even number of grooves.

 

[Patriot]

TBP,

If you're loading for a revolver, it's not so much the barrel that you need to size, it's the bore coming out of the chambers. Matching the bullet size to bore size is the most important thing you can do for accuracy. The barrel has a forcing cone and it will take care of itself. The best way to measure the bore diameter of the individual chambers within a revolver cylinder is with a set of plug (a.k.a. pin) gages. Like these.

They're pretty easy to use - just keep dropping them in one at a time, going up in size until one doesn't fit. Read the number off the last one that fit and you've got your bore (and bullet) size.

If you're loading for an autoloader or rifle, then get a soft piece of lead slightly larger in diameter than the barrel, and drive it through the barrel with a wooden dowel. Afterward, simply measure the diameter of the slug - including the protrusions caused by the rifling grooves. This is a lot easier if there are an even number of grooves.

Thanks EC,

It's not a rifle and I didn't feel like driving a plug of lead down the bore of the revolver(s)
in question. That's a pricey solution to my problem. I've emailed the seller to get the
shipping cost.

 

[Patriot]

EC,

I mic'ed the two cylinders and one is ~.312 and the other is definitely .313. Do I have to
get two different size bullets? I have shot both with standard .32 H&R which is .312. Will
the one measuring .313 suffer with accuracy problems with commercial ammo? I haven't shot
either enough (yet) to get a 'feel' for how they are shooting. It's too expensive to shoot
these suckers without getting my reloading setup in place (in process).

TBP

 

[EddieCoyle]

EC,

I mic'ed the two cylinders and one is ~.312 and the other is definitely .313. Do I have to
get two different size bullets? I have shot both with standard .32 H&R which is .312. Will
the one measuring .313 suffer with accuracy problems with commercial ammo? I haven't shot
either enough (yet) to get a 'feel' for how they are shooting. It's too expensive to shoot
these suckers without getting my reloading setup in place (in process).

TBP

In spite of what anybody may tell you, it's impossible to get a good diameter reading with a mic or caliper. I wouldn't trust what you're getting. If you have access to a machine shop or testing lab, you might be able to "borrow" their plug gages.

If the chambers are only a thousandth or two off, use a bullet that matches the largest diameter. More than that, and you'll need to experiment and compromise.

If you can find them, get hollow base wadcutters. The base of the bullet will obdurate under pressure and fill any extra space so you can use a bullet that matches the smaller diameters.

If you use a regular profile (non-wadcutter) cast bullet that is too small, you're going to get leading.

 

[jhrosier]

TBP,
Jacketed bullets in revolvers are not as demanding as cast bullets. The .312 jacketed bullets should shoot fine without any problems in a .313 bore.
It is when you go to cast or swaged lead bullets that you must be sure to oversize the bullets at least .001" greater than the bore size to avoid gas cutting, which causes leading.

 

[Bugs100]

I have a 32-20 and use .313, the company I buy them from offers Standard Sizing - .313
Optional Sizing - .309, .310, .312, .314.

If you want to pm me I will give you their name.

 

[Patriot]

More fuel to the fire....


I emailed S&W support and asked them what the two barrels are dimensioned for at
the factory as both of them are fairly unused. They told me that the Bore is .3035"
and the Rifling is .3125". I am going to measure the cylinders with pin gauges if I can
find the number of my buddy that is a machinist, but given these dimensions I would
guess that if I was using lead I would purchase .313".

TBP

 

[Gammon]

Lead bullets must be .01 larger than bore diameter; the bullet must fit the barrel, not the chamber.