Dip-Casting Bullet Weight Experiments

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TexasMac
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Dip-Casting Bullet Weight Experiments

Post by TexasMac » Fri Mar 17, 2017 8:07 pm

I just posted an article titled, Dip-Casting Bullet Weight Experiments. For some time I’ve been unsatisfied with the variations in bullets weights when dip-casting bullets for my Browning .40-65 BPCR. So I ran some experiments to identify the root cause, which turned out to be a success. For the details click on the following link: http://www.texas-mac.com/Dip-Casting_Bu ... ments.html

Wayne
NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

TexasMac
PostsCOLON 972
JoinedCOLON Sun Nov 20, 2005 6:08 pm
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Re: Dip-Casting Bullet Weight Experiments

Post by TexasMac » Sat Mar 18, 2017 10:31 pm

I posted the comments and the link to my article on several other BPCR forums & received a couple of responses that has me 2nd guessing my conclusion from the experiments. Both responders indicated that when tin is alloyed with lead, the result is a homogeneous mixture or solution, meaning the tin cannot separate, stratify & form a higher concentration in the upper portion of the pot as I suggested. Since additional research on the subject indicates that to be the case, I’m scratching my head and may have to run some more experiments to figure out what’s happening. There is a possibility that some of the weight changes could be related to a temperature stratification issue, but there’s no question that the percentage of tin in the alloy dropped throughout the casting sessions when the pot was not stirred. Regardless, stirring the alloy still applies.

Wayne
NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

TexasMac
PostsCOLON 972
JoinedCOLON Sun Nov 20, 2005 6:08 pm
LocationCOLON Central Texas
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Re: Dip-Casting Bullet Weight Experiments

Post by TexasMac » Fri Mar 24, 2017 3:40 pm

Due to the previous results of my bullet weight experiments, which conflicted with normally accepted understandings of a homogeneous lead/tin alloy mixture, I decided to run some additional tests.

1st session:
To check the homogeneous nature of the alloy, the pot was filled with 20:1 alloy, fluxed & allowed to set for 7 hrs. Using the bottom pour feature, several bullets were cast & the lead/tin ratio measured. Then, by gently filling the ladle from the top of the alloy to minimize disturbing the alloy, several bullets were cast & the lead/tin ratio measured. The ratio of the alloy from the top of the pot was 18.5:1 and 19.5:1 from the bottom.

2nd session:
The above test was repeated after allowing the pot to set for an additional 8 hrs. The ratio of the alloy from the top & bottom of the pot was 19.5 & 19.7 respectively.

3rd session:
Finally, the test was repeated after letting the pot set overnight (approximately 12 hrs). The resulting alloy ratio from the top & bottom of the pot was 18.8 & 17.0 respectively.

The above results tend to support a homogeneous alloy versus what I measured in the earlier experiments for which I have no explanation. I’m beginning to wonder if unseen voids in the bullets affect the specific gravity (alloy ratio) measurements.

But I needed to cast up a batch of bullet for an upcoming match. So 60 bullets were cast while stirring the alloy. The result was a total weight spread of 0.8grs and the average lead/tin ratio measured at the start and finish was 20.2:1 +/- 0.2, which essentially confirmed my results from previous sessions when stirring the alloy while casting.

That’s it for me. I don’t plan on additional experiments on this subject. I’ll just be sure to stir the pot during future casting sessions. By the way, a forum member reading the results of my experiments referred me to an excellent article that was published in the Jan./Feb. 1981 issue of the Hanloader magazine. Titled, Weight Variations in Cast Bullets, it can be accessed at https://www.riflemagazine.com/magazine/ ... artial.pdf.

Wayne
NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

TexasMac
PostsCOLON 972
JoinedCOLON Sun Nov 20, 2005 6:08 pm
LocationCOLON Central Texas
CONTACTCOLON

Re: Dip-Casting Bullet Weight Experiments

Post by TexasMac » Fri Mar 24, 2017 7:44 pm

Ok guys,

The light finally came on & I believe I’ve figured it out. After a little more research and another small experiment, it became clear that unseen voids in bullets have a direct affect on measurements of specific gravity (SG). Archimedes’ principal, which is the bases for SG measurements, states that “Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object”. Therefore, since a bullet will displace the same volume of water regardless of the size of internal voids, SG measurements are inversely proportional to the size of the void. I.e. when using the air versus water weight technique to measure SG, the SG of a bullet with a large void will be lower than the SG of an identical bullet with a small void. Hence, the large-void bullet measurement will imply a smaller lead/tin ratio. E.g. using a 530gr bullet cast with 20:1 alloy, if another bullet from the same batch weighs 529gr due to a 1.0gr void, the SG of the 529gr bullet will incorrectly suggest the alloy ratio is 18.6:1. Therefore, when measuring SG to determine the lead/tin ratio of an alloy, it’s wise to use bullets that fall within the upper end of the weight spread, indicating minimum voids.

So, given the above, I reviewed my data from the original experiments that incorrectly suggested the lead/tin ratio of the alloy was increasing as bullets were being cast. I found that when starting the casting sessions all initial measurements of the SG were based on bullets that were slightly lighter weight than those cast later in the session. So it’s a good bet the initial bullets had slightly larger voids, which diminished as the mould temperature increased. Although I was using a hot plate to keep the mould hot between sessions, apparently it was not hot enough.

As to why the weight spread diminished from session to session, I have no clue. It may be the result of subconsciously improving my casting and/or measuring techniques.

BTW, I now know the original experiments and my assumption were incorrect. And I’m convinced that lead/tin alloys are a homogeneous solution. The tin will not stratify in the alloy and neither will the lead/tin ratio change due to fluxing or removing the dross. Therefore I plan to remove the original article from my website.

Wayne
NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

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