Alloy vs bullet size

[cuslog]

Just came through a learning experience (for me anyway) - more experienced casters will already know this.
For a few years I cast wheel weights - worked just fine. Then got interested in BPCR (Black Powder Cartridge Rifle) and Shuetzen.
Talking to those guys - they were recommending I go to 20:1 pure lead / pure Tin. So, I tried this alloy, thinking I'd get better accuracy but I got the opposite, terrible accuracy. Mic'd the 20:1 bullets and found they were ~ .002 ~.003" smaller than the WW bullets. Searched on the ASSRA forum site and someone suggested boring out just the base band of the mold by .002 or .003". I did just that and my accuracy came back and maybe even a bit better. Long and short of it was the smaller 20:1 bullets were not sealing the bore and accuracy was terrible until I bored out the base band and then it came right back.

[243winxb]

Antimony makes as cast bullets larger in diameter, as you found out.

After sizing cast bullets, check finished diameter. Different lead alloys spring back more or less. My Lyman .357 die always made a finished diameter of .3575" Till 1 day some pure was added, produced to small a diameter. Barrel slugged at .3575"

[cuslog]

And besides poor accuracy, the smaller bullets leaded the barrel.

[Winger Ed.]

Casting is definitely a learning curve.
I've been doing it since the 80s, and I still see things that make me say, "Hmmm,,,, I didn't know that".

You may have also noticed that with the different alloys, your boolit weights will trickle up or down too.

[cuslog]

Casting is definitely a learning curve.
I've been doing it since the 80s, and I still see things that make me say, "Hmmm,,,, I didn't know that".

You may have also noticed that with the different alloys, your boolit weights will trickle up or down too.

Yes, I started laying out bullets in the order as cast and weighing every bullet - I've noticed the weights "creep up" - I thought maybe it was the mold heating up ?
Also started ladle casting - weights got more consistent and looked "cleaner" too.

[243winxb]

Adding antimony is not going to increase as cast diameter .003" Or is it.

Redding info - Bullet Sizes & Weights – How to Vary Them
The bullet diameters and weights presented in this list are based on the use of Taracorp’s Lawrence Magnum bullet alloy (2% tin, 6% antimony, 1/4% arsenic, 91.75% lead).

Bullet diameters and weights will vary considerably depending on the lead casting alloy used. This variation can be as much as 1/2% on the diameter, and 8% on the weight among the most commonly used casting alloys. For example, a .358-158 grain bullet might show a diameter variation of .002", and a 13 grain difference in weight.

Of the most commonly used alloys, wheel weights (.5% tin, 4% antimony, 95% lead) will produce bullets having the smallest diameter and heaviest weight, with such bullets running approximately 1/3% smaller in diameter and 3% heavier than bullets cast with Taracorp's metal. Linotype will produce bullets with the largest diameter and lightest weights. This alloy will produce bullets approximately 1/10% larger and 3% lighter than Taracorp. Other alloys of tin and antimony, with antimony content above 5%, will produce bullets with diameters and weights falling between those cast f rom wheel weights and linotype.

Alloys containing little or no antimony will cast considerably smaller than wheel weights and in some cases will produce bullets too small for adequate sizing.

Within the limitations given above, the weight and diameter of a cast bullet can be adjusted by varying the
alloy’s antimony content.

The size and weight of bullets of a given alloy will also vary according to casting temperature. Higher temperatures will result in greater shrinkage as the bullet cools, thereby producing a slightly smaller and lighter bullet than one cast of the same alloy at a lower temperature.

[Winger Ed.]

- I've noticed the weights "creep up" - I thought maybe it was the mold heating up ?
.

I'm not sure about that, I never tested the idea or heard of it being spoken of.
It's a given that different alloys will drop boolits of slightly different weights.

Something I learned here that I'd never thought of before:
I'm not sure how long it takes for various other things in molten Lead to stratify out like dirt mixed with water---
but I'm sure they will, and that'll have an effect on boolit weights changing within one pot that isn't stirred enough.

[Outpost75]

Accurate Molds and Roto Metals web pages have info on alloy vs. casting diameter.

[mfraser264]

Diameter change by alloy, RCBS Cast Bullet Manual #1, page 13.

Attachment 291892

[kevin c]

My metallurgy-fu is weak. I see, in mfraser’s chart, that compared to 1:10 and WW, linotype shrinks less (+ .0007”) and pure shrinks more (- .0011”). Does that mean a linotype boolit from that mold will be .0018” bigger than a pure lead boolit from the same mold?