How much does lead shrink from hot to cold?

[bennypapa]

I was thinking of making some bullet molds but it occured to me that lead has to have some expansion/contraction from hot to cold. Does anyone have any data on how much bigger a mold should be to arrive at a certain size when cooled?

Bennypapa

 

[Old Ironsights]

Not enough to worry about. That's why you rarely hav to worry about "fill-out" when casting with pure lead, but do with alloys.

The melting point of lead is 327.35°C, and the boiling point is 1515°C. The only common metals with lower melting points are tin and bismuth, while the boiling point is high enough to allow processes in liquid lead over a wide temperature range. The coefficient of linear expansion is 29.5 x 10-4 per °C. The bulk modulus is 0.44 x 106 Mbar. The heat conductivity is 0.081 cal/cm-s-°C, and the specific heat is 0.03046 cal/g-K (all properties are room-temperature values). The heat of fusion is 6.26 cal/g. The electrical resistivity is 20.648 μΩ-cm (compare to copper, 1.683). The hardness of pure lead is 1.5 on the Mohs scale (between talc and gypsum: it can be scratched by the fingernail), and its tensile strength is only 2000 psi. The Young's modulus is 2.56 x 106 psi. Its crystalline form is face-centered cubic, with lattice constant 0.4939 nm. Lead alloys considerably with bismuth and tin, to a smaller degree with antimony and silver. Lead anneals itself (rerystallizes) at room temperature, so cold work does not harden it.
[url] http://www.du.edu/~jcalvert/phys/lead.htm[/url]

 

[Bob Riegl]

:grin: Wow, talk about verse & text from The Handbook of Chemistry. The big factor here is the coefficient of linear expansion which is measured to the ten thousandth place. Generally we have to examine the liquid hase to find coefficients in several orders of magnitude > Pb(s). :yakyak: :rotf:

 

[bennypapa]

Looks like I'd have to be making very large objects with really tight tolerances before it would add up to enough to matter.

Thanks for the extremely informative response.


Bennypapa

 

[Slamfire]

Generally speaking lead alloys will shrink a bit more that just plain lead. :winking:

 

[guncobbler]

I Like the tongue in cheek comment at the end of Ironsights link to the lead properties site:

"Lead is still used for sheathing cables, in bearing alloys, in artistic pigments and glazes, for decorative glass, in the chemical industry, and, of course, for bullets, which have always been in special demand in the United States."

GC

 

[dlemaster]

Slamfire
Actually it is just the reverse. I found this out casting bullets for a Sharps .45-110. In the mould I had made for 500 grain bullets of 20 to 1 lead tin mix at .459 dia, I found that pure lead cast in that mould at .458 dia. Bullets cast from Linotype (a very hard alloy with tin and antimony) cast at about .460 dia.
Check with any of the serious BPCR shooters or their web sites for a explanation on the rates various alloys shrink from the same moulds.

Regards, Dave

 

[bennypapa]

On this page

http://www.lasc.us/CastBulletNotes.htm

pure lead is listed as having 1.13% shrinkage.

0.490 x 1.013 = 0.49637"

To me 0.006 is indeed significant. Much more than I had thought. If I make some molds I'll have to take that into account.

 

[paulvallandigham]

Bennypapa: Sorry, but you did the calculation wrong, thee buddy.

It should be: .490 x .0113 = .005537 !

55 hundred thousandths of an inch is what I would call insignificant.

 

[bennypapa]

You're right on the math but...

We're talking about 0.0055"

I'd drop the 0.0005 for the sake of this discussion and say that we are dealing with a difference of 0.005". That is the same as the difference in a 490 ball and a 495. Isn't that enough to notice when starting a patch/ball?

If I need a 0.490" ball and make a mold at 0.490" the ball will be .490 x (1-0.0113) = 0.484463 rounds to 0.484

I'll admit to being a newbie at this game so I'd like to ask, what practical, user noticable difference would I find if I normally use a 0.490" ball and patch combo that starts well and shoots well, then tried a .484" ball with the same patch?

Please note, I am trying to learn, not argue so I hope this doesn't sound argumentative.

Thanks for the input,

Bennypapa

 

[paulvallandigham]

In reality, you don't get that wide a variance with cast balls. IN fact using " Pure " lead( there is always some small amount of impurities) its often difficult to get the balls to drop out of the mold! Using alloys, you get balls that shrink enough to drop out fairly easily. But, I am talking about bullets cast from pure lead vs. 20: 1 allow, lead to tin. 5% tin is a very small amount of alloy, but enough to raise the melting point, and change the shrinkage characteristics. You are going to have more trouble with air bubbles in your lead, than you will with dimensional difference due to casting shrinkage. That is why we weigh round ball. for plinking, don't bother. For hunting large game at reasonable range, you can sort to plus or minus 5 grains in the larger calibers, and plus or minus 2 grains in 45-54 calibers. Under .40 caliber, you will do better to sort to plus or minus 1 grain. And, for serious target work, sort plus or minus one TENTH grain, or less. When you are working with pure lead, the ball upsets on firing and obturates to fill the lands and grooves of the barrel, forcing the cloth patching into the grooves ahead of it. But the shape and size does change in the process of firing. That is why a variation of up to .001 inch just doesn't matter as much as the total weight, and presense of wrinkles, or air bubbles in the round ball.

Paul

 

[bennypapa]

That is the kind of practical application knowledge I need. I can just imagine my pristine ball in the barrel as the powder charge gies off. If I can scratch it with my fingernail, surely it will deform as it is fired. Makes sense.

Thanks

 

[paulvallandigham]

If you ever join the " Dry-baller's club ", a distinguished group of BP rifle shooters that includes darn near everyone who has been shooting for more than a year, You will see after pulling a ball how the ball deforms into the rifling, and how the soft lead wears the weave pattern of the cloth patching. If you have six lands and grooves for rifling, the ball will take a six sided appearance when it comes out of the barrel. I joined that club many years ago, and Murphy sees to it that I re-enlist every so often, just to keep my humility bright and shining!