How much CERROSAFE do I need?

[hunter64]

I have a couple of .303 brit No.4's that I am having a heck of a time trying to get minute of 4'x8' piece of plywood accuracy with. I have tried slugging the barrel and one is .313 and the other is .314. Played with lots of combinations and having read lots on this web site I have finally decided I need to break down and buy some cerrosafe and see exactly what my chamber is on both of the rifles. So for you that have used it will one pound be enough to make a chamber cast in a .303 or do I need more than that?

[MtGun44]

Way plenty, unless you plan on keeping the casts for reference.
If you cast, measure and remelt, it'll be enough for about
4 or 5 or more unless you cast well down the barrel. You
DO want to cast the throat so set your patch about 2"
deeper than the end of the chamber.

The stuff tends to wet glass, I have had better luck with
a metal melting container - but I forget what it was made
of, just that it tended to stick to and leave a film of metal
on a glass beaker that I used the first time. Follow the
instructions on measuring TIMES also, as the stuff changes
dimensions in a predictable way, but you need to measure
WHEN it is right, relative to when it solidified.

Bill

[hunter64]

Mtgun44: So 1/2 pound will be all I need? I just want to do one measure it and then reuse it.

[44man]

This drives me nuts!!!!:( I had this all printed and the power went off for a second, shutting me down.
Anyway, the stuff is only good for seeing the chamber and throat. There is enough to do a bunch with what they send in one order. I use a soup spoon with a pour spout bent in to melt and pour.
You will never get the right dimensions from the stuff no matter when you measure it. I have used it for years and it is always wrong. A lead slug upset in the barrel is the most accurate way to measure unless you are rich and can buy an air gauge. I would not waste money on Cerrosafe if you are looking for accurate measurements. I have experimented with a known bore size and the stuff is NEVER right. There might be a 5 second window where it is but I have not found it.

[44man]

45 2.1 told me how to measure the chamber. I put a brass rod in a case, seated a pure lead boolit, chambered it and dropped a brass rod down the barrel. Using a large hammer, I expanded the slug and case mouth. This gave me the neck and throat measurements. It was way different then the Cerrosafe stuff gave me.

[sundog]

I use sulfur with some graphite mixed in. Very lightly oil the chamber and throat, pour in the liquified sulfur and let cool. Perfect chamber cast every time. Caution - be careful heating the sulfur as it can ignite easily.

[NVcurmudgeon]

I only used Cerrosafe once, to send a chamber cast to a honcho for a grup buy that collapsed. Melting the Cerrosafe in a Coca Cola aluminum can worked well.

[alamogunr]

Here is a good "How To' with pictures:

http://www.surplusrifle.com/shooting2005/chambercast/index.asp

[montana_charlie]

So 1/2 pound will be all I need? I just want to do one measure it and then reuse it.I bought a single ingot of Cerrosafe to make a chamber cast for my .45/90.
I cut off a third of the ingot and melted that. It was easily more than I needed for the cast.
I have used the stuff to:
- cast a 'hard' bullet for compressing powder
- model the interior shape of cartridge brass
- duplicate an engraving pattern

Since I keep remelting the stuff for different projects, I wound up sending the unused half of my original ingot to a friend.

A word about the accuracy of Cerrosafe dimensions...
I won't claim that casts are predictable for getting accurate measurements, but custom bullet mould makers rely on it.

They provide instructions for making the cast and protecting it during shipping, and they want to know when it was made.
Using their knowledge of how it changes, they then produce a mould that matches the customers gun.

Someone like Paul Jones or Steve Brooks would not be able to stand behind their $200 moulds unless Cerrosafe was predictable enough to give them good information.
CM

[MtGun44]

Yes, for a single cast, 1/2 lb will be way plenty.

I have used it to inspect blank-firing machine gun chambers
to verify the safety modifications at work and to inspect throat lengths
on a few of my own guns. I have never attempted to get accurate
throat dimensions. It is great for 'taking a look' inside a chamber and
throat and bore, but I cannot personally vouch for the precision
of the cast relative to the actual bore.

Others report good results and a few report bad results. I suspect
that casting techniques and measurement methods throw a lot
of variability into the process.

Bill

[44man]

Most of the time the casting dimensions are greater then the actual bore size and that is not a bad thing when making a mold. We all know a larger boolit is better so the custom makers can justify using the casting by subtracting expansion rates. This gives a boolit a little over bore size.
Many slugs expanded in my bore show .4593" but a casting will show .4608", does shooting a .461 to .464 boolit make it bad? NO! Much better then a .457 or .458 boolit. This is where the custom makers shine, giving you a boolit that is not too small.
If you want the actual bore size, don't use Cerrosafe but you CAN fit a boolit with it.

[hunter64]

Thanks guys for the replies, the "How to" was very good and seems easy. I think I will order a 1/2 pound from Brownell's and give it a whirl.