Using lead to measure barrel volume

[dbooksta]

In order to test a hypothesis I need to very precisely determine the (relative) volume/length of a few .30" barrels. The barrels are a mix of stainless, 4140, and nitrided 4140 steels.

The best approach I can come up with is to plug the breech of the barrels and pour in a liquid to measure the volume over a given length. The liquid should have low surface tension against steel so that it fills the grooves completely.

So I was thinking that pure lead would be ideal for this because it tends not to hold air bubbles and tends to fill out steel cavities nicely. If I fill each barrel with pure molten lead and wait for it to solidify, then I am assuming I can tap it out, cut the slugs to equal lengths, and weigh them to get a comparison of bore volume.

Questions:

1. Is molten lead the best liquid for this purpose? Any easier ideas?
2. If lead do I need to precoat the barrels with a release agent, or will it shrink as it solidifies enough to detach?
3. Can I tap this extended slug out the muzzle from the breech with a bore-diameter rod? Or is there a risk I'll shear it and leave strips of lead against the rifling, and if so how can I get the solidified slug out?

If I were to use a liquid that stays liquid I would need one that is non-wetting for steel (or whatever release coating I can put on the bore) and that has very low surface tension (so that it doesn't retain air bubbles). I would also need a method to plug the bore very precisely so that the length of bore filled by the liquid is identical, probably to the hundredth if not the thousandth inch.

Any thoughts or advice appreciated!

[Cap'n Morgan]

Forget about using lead! Surface tension is too high to get a reliable fill-out and you'll have to re-melt the lead to get it out of the barrel.

Much better to slug the barrels and then use math to determine the volume. It's not all that hard to calculate the bore area once you have the bore/groove diameter and the width of the grooves/lands.

[dbooksta]

From a traditional ball slug I don't believe I can measure groove width and depth to enough precision. These are all 5-land .308 barrels. I am expecting cross section variance to be third order at best.

[Bent Ramrod]

Mercury might work. You'd have to clean all the oil out of the bore and securely plug the chamber. The only variable would be the meniscus at the top.

That's the only liquid I can think of that would cover every surface and yet have a chance of completely running out afterwards. Anything like an oil or water mixture would leave a film that would evaporate or cling to the surface without completely running out.

You would have to do your measuring under temperature controlled conditions to make sure the mercury is at the same density, otherwise you will get different weights for the same volume.

[Doc Highwall]

Question as to why you need a such a precise measurement that will be affected by temperature? Why would not just using math do what you need?

[dbooksta]

I don't think the temperature variations in my workroom are a problem.

I guess I could try to use a ball slug and see if I can calculate a difference with a micrometer based on the land diameter, groove diameter, and ... what, an eyeball estimate of the fraction of the circle cut by grooves?

One thing I'm unsure of is whether the variation in cross section along the length of a bore is of the same magnitude as the variation in cross section between bores. These are button-rifled production barrels, not air-gauged match barrels. A ball slug only samples a tiny length of the bore.

[theperfessor]

I'm not a chemist but I do remember from chemistry class that we measured volume by using a graduated cylinder with a drip valve. Fill it to zero (at the top of the cylinder) and then read the height/volume after filling the object. There are a number of fluids that could be used, I'd probably try water soluble cutting fluid - low surface tension and no rust problems. Any high schools around you have a chem lab?

I definitely would not fill a barrel full of melted lead.

[GhostHawk]

I was leaning more towards brake fluid or ATF myself.

I don't think I'd use lead. Too easy to get voids, probably wouldn't get good fill in unless the barrel was preheated to 500 or so.

[dbooksta]

Good ideas on the fluid! In this case I need to be able to plug the bore at a very precise depth.

So let's assuming I'm going to be measuring water-soluble cutting fluid into the muzzle. What could I use as a flat-faced plug inside the bore to mark a precise depth? This would have to be positioned past the leade since I'm only interested in the fully-rifled segment.

[Pb2au]

Fill tank with water. At the high level of the water, have an over flow port feeding to milliliter graduated beaker.
Put barrel into tank. Record amount of water displaced into milliliter graduated beaker. Call it measurement A.
Remove barrel. Refill tank.
Seal the muzzle and chamber of barrel with tape.
Place barrel into tank again. Record amount of water displaced again. Call it measurement B.
Volume B minus volume A equals fluid displacement of bore. Convert from milliliters to what ever you like. quarts, CC's hogsheads, pecks, gils,........

[theperfessor]

How about seating a round nose bullet out far enough to engage the rifling, and then carefully file off tip back to where rifling marks start?

[Cap'n Morgan]

If you will measure the volume with water it's much easier to weigh the water (and container) before you pour it into the barrel. Subtract the weight of the remaining water/container. You now have calculated the precise amount of water in the bore without having to pour it out again. If you use metric measurement, one gram is equal to one CC (cubic centimeter)

[dbooksta]

Fill tank with water. At the high level of the water, have an over flow port feeding to milliliter graduated beaker.
Put barrel into tank. Record amount of water displaced into milliliter graduated beaker. Call it measurement A.
Remove barrel. Refill tank.
Seal the muzzle and chamber of barrel with tape.
Place barrel into tank again. Record amount of water displaced again. Call it measurement B.
Volume B minus volume A equals fluid displacement of bore. Convert from milliliters to what ever you like. quarts, CC's hogsheads, pecks, gils,........

Very clever! Should probably use cutting fluid or some other non-wetting fluid to avoid the problems associated with surface tension, like tiny air bubbles inside the bore.

[John Boy]

Water at 77 degrees F is the standard to measure cubic inches.
Mercury would be expensive for this barrel determination
Use CerroSafe plugging the chamber. Cerrosafe has a melting range from 158° to 190° F. Overheating may cause separation of the components of Cerrosafe alloy.
* Clean the bore with acetone and dry.
* Pour it hot into the clean heated bore.
* When solidified, quickly heat the barrel and drain the liquid into a pre-measured container
Then use the standard cubic inch formula of a cylinder and do your calculation per length

http://www.rotometals.com/product-p/...oint158190.htm

[Coffeecup]

I'm lazy. I think I'd just go with the approach of /weighing the plugged barrels/ then filling them with the liquid and weighing them again. Some quick math would give you your answers.

[flyingmonkey35]

Do you have a local college close by?

If so give their engineering proffser a call and see if you can make it a class project.

If you don't mind the wait.

I'm not saying you can't do the math.

But that is a interesting puzzle.

They may even have access to a laser lab that can record the exact diameter on the barrel + grooves.

Just a thought

[Ragnarok]

Just fill it with water and measure the water....

[dbooksta]

Water has surface tension, which can trap tiny bubbles. Could get around that by using a surfactant, but then there's still the problem of how to plug the barrels to a precise point.

So far Pb2au has the most likely to succeed method assuming slugs don't provide adequate precision.

[Possumcop]

Why not use CerroSafe to fill the entire bore?

Making precise, removable casts is pretty much what it's designed to do.

It shrinks when it first cools to allow easy removal and then re-expands on its own. Measurements taken an hour after the original pour are supposed to be the most accurate.

If for some reason you had a problem removing a cast, you could just "borrow" your wife's blow dryer to re-melt it, then pour it out of the barrel.

[dbooksta]

That does look promising. Is the Roto158-190F alloy the best for this purpose -- where best is defined as providing the most precise, constant-density, void-filling casting, as well as the ease of removing the solidified casting without losing mass to barrel adhesion?