chamber cast Vs. slugging?

[troy_mclure]

what will slugging give you that a long chamber cast wont get you?

[Ricochet]

It'll tell you if there are loose and tight spots down the bore, and where they are.

[rob45]

Use a chamber cast to get chamber dimensions; a slug to get the bore dimensions.

As mentioned by Ricochet, pushing a slug through the bore allows you to feel any constrictions.

[44man]

I never got accurate readings with a casting no matter what is said on the instructions.

[rob45]

I never got accurate readings with a casting no matter what is said on the instructions.

44man,

I agree with you; the slugging method provides a more precise result. But I think Troy may be asking the question concerning a fixed (integral) chamber, not a revolver chamber. That's why he asked about a "long chamber cast". A chamber cast is the easiest method to measure those types of chambers, and perhaps Troy just wants to know why it is necessary to slug the bore if he can simply pour in farther to the bore at the same time he is making a casting of the chamber.


So...

Troy,

If you're measuring bore/groove dimensions, slugging is probably the better method.

If you're measuring a cylinder mouth on a revolver, slugging is probably the better method.

If you're trying to get dimensions of a (fixed) rifle chamber, the casting is the way to go because no amount of reasonable pounding will reliably swage the lead to truly fill the chamber. But don't think that simply pouring in more will also give you an accurate reading of the bore, because once that casting engages the rifling it will take the hammer of Hades to get it back out if you have poured far enough for the twist to become fully engaged. If you poured that much, you're probably going to have to melt it back out! So plug the bore slightly after the point where the rifling begins.

As 44man mentioned, getting accurate readings is difficult- that is because you have a very narrow time window in which to take your measurements, and the expansion/shrinkage factor is highly dependent upon the alloy content, which can vary according to the quality control standards of the manufacturer. In other words, the method of chamber casting introduces too much room for error. The only times I use the chamber cast is when I want an idea of neck clearance (outside neck turning as part of forming custom brass) or want an idea of how long the throat is.

In short, use a chamber cast for a difficult-to-measure chamber, and slug everything else.

[Shiloh]

I never got accurate readings with a casting no matter what is said on the instructions.

Yep,

Years ago we took several measurements. All dimensions were different.

Shiloh

[44man]

I make chamber casts once in a while, I just don't depend on readings anymore. The stuff seems to expand more then what is said.
I will test it someday but I think we need to measure the casting sooner after casting.
I have also thought about the best temperature to melt it at but if too cool it will not fill out, like a cold boolit mold. If too hot the chamber can expand and throw off readings. I don't think it is right to pour hot stuff in a gun for measurements.
I know if I expand lead in a bore with two rods and push it out, I get a far different measurement then a casting will.
It is the same as when I turn a cherry for a mold. After a cut, I let the metal cool before measuring. Can't measure hot metal.

[blackthorn]

I assume we are talking about casting with Cerosafe and not a Sulfur or Sulfur-Graphite cast? My understanding is that casts using Sulfur are not prone to change at all! What you see is what you have.

[montana_charlie]

It' not uncommon for a custom mould maker to ask for a Cerrosafe chamber cast of the gun he is about to cut a mould for. You probably can't get that to him quickly enough for him to take the measurements at the one hour point.

So, it must be possible for him to mathematically figure out proper dimensions while working from a cast taken a week (or more) before. It can be done if you have the formula.

CM

[leftiye]

They only expand a thou or two.