Bullet Shrinkage???

[fc60]

Greetings,

I have a mould that produces a 0.402" diameter with 20:1 alloy.

Will casting with 30:1 offer a smaller diameter bullet? i.e. 0.401"?

Or, what about 40:1, if anyone has data.

Cheers,

Dave

[Dusty Bannister]

It is the presence of antimony that affects the rate of shrinkage.

[Rcmaveric]

Different alloy blends produce different size bullets. Has to do with solidification process and how the crystalline grain structure grows. Antimony prevents shrinkage.

Most molds are designed for certain alloys. I think major mass produced brands are designed for Lyman #2 if you go to their product page it tells you or an email will get you the answer. Custom outfits you can specify your allow and get your mold designed for what ever scrap you commonly use.

A softer bullet will drop smaller and harder bullets will make larger. Sadly i once used a hard alloy in shot gun slug mold. Almost broke the mold getting it out. The slug was so badly stuck.

I know there is documentation of it some where. Judt can't remember where it is. I think maybe either LASC or From Ingot to Target.

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[TomAM]

30:1 will cast over .0005 smaller, and 40:1 a bit smaller than that.
Tin has a big affect on shrinkage. Antimony not so much.

[Dusty Bannister]

I was going by the reference in Lyman Cast Bullet Handbook, 3rd ed page 58. It does not address the various ratios of tin to lead however. Various sources indicate that tin does improve fluidity but much more than 2% is unnecessary. Interesting. In reality, does .0005" difference in diameter actually make any difference on the target unless all the other precision practices are followed?

[fc60]

Greetings,

Thanks to TomAM for my answer. I will mix up some 30:1 and cast some new bullets. It is a Paul Jones mould and I would like to put it to use.

The issue I have is the 20:1 bullet does not enter the barrel without undue force. I am shooting a BPCR rifle.

"TomAM", sort of rhymes with Tom @ Accurate Moulds?

Cheers,

Dave

[243winxb]

Maximum heat will cause more shrinkage & product frosted bullets. Ok in iron molds, not in Lee.