best way to measure chamber thoats?

[waco]

all i own is a set of dial calipers
do i need a plug gauge set?
i dont think the calipers will give an accurate enough reading
how do you guys do it?

[Rocky Raab]

Plug gauges are probably best unless the cylinder mouths are also out of round. A Cerrosafe casting is good either way. Calipers might be okay, but a micrometer is better for this kind of measuring.

[Edubya]

Some where on this site someone wrote about using a sulfur mixture instead of Cerrosafe for a casting of the cylinder/throat. It sounded good and was less expensive.
I kept the article on my old computer and I can't find it now.
Good Luck,
EW

[BABore]

A good 0.0001 resolution micrometer is a good start. Calipers aren't the best way to measure diameters. Adding a height gage so you can scribe reference points on your slug for measuring is a fine addition. The best device is a Starret optical comparitor with digital readouts. I got to measure a boolit profile on one of those recently and it was Sweeeeet!

[Edubya]

Here is the thread I was looking for:http://castboolits.gunloads.com/showthread.php?p=677451
buckthorn;"An alternative to using Cerrosafe is to make a sulphur/graphite cast. To do this, make up a mixture containing a ratio of approximately two-thirds sulphur to one-third powdered graphite. Sulphur requires a much higher melting temperature than Cerrosafe but it has the advantage of neither growing nor shrinking once the cast has set."
EW

[Cap'n Morgan]

This is how I measured the throat on my 45-70 Uberti 1885: A couple of 6.5 x 55 cases was turned down to fit snugly into two 45-70 cases. The bore/grove measurements are .451/.457 The rim on one case was turned to .458, the other to .4515. After assembling the cases, each unit was carefully inserted into the chamber and the breech was closed. By measuring the overall length of both units I got an exact "picture" of the throat to use for designing a bullet which will fit the throat exactly.

http://img200.imageshack.us/img200/5282/img01qg.jpg (http://img200.imageshack.us/i/img01qg.jpg/)

http://img97.imageshack.us/img97/1226/img02j.jpg (http://img97.imageshack.us/i/img02j.jpg/)

[Lead Fred]

http://www.varmintal.com/arelo.htm

case and chamber measuring. I bought sinclair plugs.

[joeb33050]

So far you guys are talking about 2 different things, the Max OAL and the chamber dimensions.
Max OAL is involved. Quite involved.

Chamber dimensions, slugging the chamber, is easy.
Clean well and lightly LIGHTLY oil the chamber and bore.
FL size a case with a fired primer in it.
Bell the dickens out of the mouth.
Put bullet/s in the case. For a 308Win I put in 1 31141 and 1 314299. At the same time, melt the bullets with a Bernz O Matic torch. You want a case with lead filling it to around the bottom of the neck.
Get a bullet without a lot of grooves on the top. 314299 with a long nose will work, if the height of lead in the case is correct. You want the nose to swage into the chamber, with no grease grooves fouling up the chamber slug.
Start the bullet in the case.
FL size the case and bullet.
Put it in the chamber. This may require a LITTLE hammering to get the breech closed.
Get a steel rod from the hardware store. For 30 cal. I use a 1/4" rod.
File one end of the rod so there's no burrs.
Masking tape that end so it's a nice fit in the bore.
Tape every 6" or so, to center the rod and keep it from hitting the lands.
TAPE the rod at the crown, we don't want to hurt the crown.
Put the rod in the barrel, pound the end with a hammer. You will feel when it has slugged the chamber, the rod will sort of ring.
Rod out, ctg. out, measure and draw a picture.
I have done this a lot, and it recently took 4 tries to get a slug that I believed in.
Good slugs have ~1/2" of the bore on the end.
I use a 6" caliper and 1" micrometer caliper to measure, and draw a picture, and write it all down.
I take my time, and am very careful. I have no mechanical ability, so I have to.
joe b.

[joeb33050]

Here is the thread I was looking for:http://castboolits.gunloads.com/showthread.php?p=677451
buckthorn;"An alternative to using Cerrosafe is to make a sulphur/graphite cast. To do this, make up a mixture containing a ratio of approximately two-thirds sulphur to one-third powdered graphite. Sulphur requires a much higher melting temperature than Cerrosafe but it has the advantage of neither growing nor shrinking once the cast has set."
EW
I have made many sulphur chamber and bore castings. Sulphur is available from your pharmacist. He'll order it and it's cheap. I find it difficult to make a sulphur cast in a bolt gun. Single shots like sharps or maynards or 44 1/2s are much easier. Bolt guns end up with hard sulfur in the action, and are a bear to get out.
Sulfur chamber castings are about .001" SMALLER than lead slugs in the same chamber. I've found this enough so that I now rely on lead slugs, and let my sulfur rest. I never added anything to the sulfur.
joe b.

[coyotebait]

waco
If you are talking throats on a revolver, just push an oversize bollit through each throat and measure with an accurate (.0001) micrometer. A 0-1" mic should be on every reloaders bench IMO.

coyotebait

[Shiloh]

Sulphur is also very reactive with just about everything. Could it react with the alloys in barrel steel as well??

I'm not sure I'd want to chip it out of a chamber or throat.

Shiloh

[sundog]

Joe is right on with the sulfur (and micro graphite) for chamber/throat casts. Works great. For a bolt gun I use a piece of poly tube that fits the bolt race and snugs up against the chamber opening, and a funnel to get it in there. Works pretty good if you are careful. VERY light coat of light weight oil in the chamber helps extraction.

Only downside to the sulphur is chance of it flashing off (no open flame to heat) and odor. I've never had a problem.

I don't care for pounding on a good rifle. In fact, instead of slugging the bore, I just use successively sized boolit until I find one it likes. Of course, having a good selection helps. BUT, you could always beg a handful of something here of the board just for asking.