Shrinkage while casting Lead or Zinc

[BoomLover]

Just wondering what percentage of shrinkage to expect while casting Lead or Zinc. I have heard that there can be as much as 10 to 15%. Asking because I aquired a double mold that supposedly casts 1 1/2" balls, but the cavity measures 1 5/8". The balls that came with it actually measure 1 7/16th". Is this a reasonable amount to expect for shrinkage in casting these metals? Thanks, BoomLover

[GGaskill]

10-15% shrinkage is way more than I would expect for either lead or zinc castings.  More like 1-2% in my experience.  One thing that you must keep in mind when casting zinc or lead (but especially with zinc) is that the casting will continue to draw metal while solidifying and the sprue MUST be kept liquid until the casting is solid or it will have internal voids.

We cast about 30 2.6" zinc shot at the Montana Shoot and had to play a propane torch on the top of the mould to make sure the casting was true.  Depending on how long we let the filled mould cool, the shot would fall from the mould or need to be whacked with a stick a few times to remove it from the mould.  So it certainly wasn't 1/8" smaller than the mould cavity.

I think you will have to cast a few shot to see what you actually get.  One warning; once you have cast zinc in the mould, it will not cast clean (meaning shiny surface) lead shot.  This is a problem with small arms bullets but probably not a problem with cannon shot.

[armorer77]

Hi Boomlover , I had my GB mold cut at 1.690 , this casts a 1.680 ball . My 75 cal mold is .735 which throws a consistant . 733 ball . I am casting plain wheel weights . Armorer

[nematode]

Pardon my intrusion since some good answers have already been posted. If you contact Ney Smelting at the following link http://www.neymetals.com/ and ask to speak with one of their metallurgists, they will be able to advise you on shrinkage and many other important aspects depending on size of your casting and alloy being used. Herb Doyle is the guy that has helped me so much over the years - ask for him if you want a name. Great guy and true professional.

[BoomLover]

Thanks  all the responses! This tells me I should sell this mold to a fisherman for cannon ball fishing weights, and go look for a true 1.5" mold. Here I thought I got a good deal for my $10! But if it won't fit any of my barrels, it's no use keeping it! 1 to 2% sounds a lot more reasonable for shrinkage. I have purchased ready-made so far, thought with a bucket of Lead and a bucket of Zinc, I'd try to cast a batch. This forum has it all, thanks again! BoomLover

[nematode]

Boomlover, I worked in almagam research for a well known dental company years ago. During that time I cast many ingots and special samples in a variety of molds and applications. Alloy was bronze and other varieties including high silver content. Since 1989 I have cast miniature animals in pewter, thus my connection to NEY Smelting, mentioned above. I'm only tacking on a second response to let you know that depending on the alloy formulation, volume, mass and cross-section thickness of cast parts and casting temperature, shrinkage can vary. The main thing I want to share is that having cast more than a thousand sculptures in pewter, experimenting with different pewter alloys but mainly using NEY's DB alloy, whether the piece was a tiny half inch bird or a larger 6" chunk cast weighing 2.5 pounds in solid pewter, never, ever, did any of my castings shrink so much that gap or separation between casting and mold could be observed. No surprise that your 1 5/8" castings are too big for 1.5" bore - no way to shrink that much! You're on the right track - best wishes.

[dynomike]

I bet i have one of those $75.00 moulds to. Mine was advertised to be 2.25" and it's actully 2.125" i called him about it and all he did was loose my busisess.

[BoomLover]

This one was advertized at 1.5", actual measurement was 1 5/8th", (of course, I took him at his word) but he included 2 balls, which measured 1 7/16th". As you can see, a 1/16th" shrinkage is within range, but, after all the final measurements were in, it was a "no go"! Hummm, I'd say that there was a bit of a discrepency in the stated sizes! I won't lose anything on it, 'cause I can re-sell it, however, I'll have one made that is proper 1.5" just to be sure! Or try another dealer, for sure! BoomLover