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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...periments.html
Wayne
Interesting test and a good write up.
Question: Do you think the lead / tin ratio would change from the top of the pot to the bottom of the pot? (Assuming it was properly mixed, fluxed then allowed to "settle"?
Thanks for sharing your knowledge! I found the article enlightening!
For the record, I'm a new caster. Tonight I managed a weight difference of 1 gr +/-, 500 gr 45-70 bullets (30-1 lead) in a random quality check, about every 20 boolits. (weight average 508 before lubing)
Mold was a Lyman 457125.
I have found with these big long bullets the ladle pour and over pour gives me the best results. Getting the lead in hot and at the right flow so the bullet is molten completely Is achieved easier for me. I don't pour a sprue but a ladle full of lead letting the excess run back into the pot. This keeps the bullet, base. and sprue plate hot as long as possible giving good looking sharp bases and sharp corners. Ive been as good as a 1 grn ( +/- .5 grn) variance over a 4 hour session. A little experimenting with your mould and technique helps consistency a lot also.
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
Hello Wayne, It will be interesting to see what you come up with. Because the various opinions on this, some founded in metallurgy and some in repeated internet wisdom I chose to not respond earlier.
I think I will just stick my toe in.....
This subject rhas had my interested for decades because of the conflicting ideas that get floated. I used to have dinner with Bill Ferguson 10 plus years ago when he would attend the AZ longrange matches and his opinions agreed with Art Green, who would talk you ear off when you called and ask questions. I consider them two good sources of info.
Me, I just restate what I think I know and site the sources......
I think you are on the right track, you can not separate the tin and lead nor will it settle out but something is causing noise in the data. Additionally, at 800 F, tin and lead oxidize at roughly close to the same rate. In other words, dross of a tin-lead mixture will be close to the same ratio as was the base metal.
For what it is worth, I have tracked my casting for match bullets, plotted the weight changes as cast and have had much the same experience you have. I have not done anything like the SG testing you have. That was interesting to read.
Because I can cast well enough, I gave in to just having match quality bullets that I am sure are good enough to win if I do my part.
I have cast and shot my share of Lead-tin bullets but you may know,( or not) I mostly like Pb-Sn-Sb alloy for my BPCR bullets now.
Thank you for sharing all the work you put in on this and other areas of casting, loading Black and the Browning rifles. You are always a thoughtful writer and tester and it make for a good read.
-Michael Rix
Hi Wayne
I have years of production diecasting experience with zinc alloys
And magnesium alloys------both use mechanical mixers in the holding pots to assure uniform alloy composition-------
Dave
One thing Ive taken to doing when casting now is when filling the ladle I push it to the bottom of my big pot and make a "swirl" with it to mix and fill the ladle with the hot alloy. This swirl is probably about 6"-8" in dia and seems to keep things more consistant for me. Maybe a low speed mixer with just a flat blade and back and forth motion to constantly agitate the pot
have you checked for air pockets in the cast bullets?
what's helped me with that issue is to unload the entire, full ladle into and over the mould - this helps even out the heat and to release any trapped air that's typically present near the sprue hole. that and doing a consistent angled pour into the mould and continue pouring 'til the mould is vertical, then just unload the entire ladle's remaining lead over the sprue hole.
Good read and thanks for sharing.
I am a dipper since I'm relatively new to casting. I think dipping might stir the pot. :)
I am just dropping some casting porn here from over the week-end. :) 500 gr 30-1 boolits using a lyman 457125 mold.
Those look good!
I was (and still am) a big fan of the design. I used it to move my way from never ever silhouette match shooter to master class. Great bullet!
Even tho we get wrapped up in good, better, best bullet design, the so called improvements are small and the Lyman 125 remains is as good as it ever was. And that is pretty good!
The alloy that is inside the pot is not a SOLUTION, therefore it cannot be perfectly isotropic. Solidified tin and lead alloys are actually a solid MIXTURE and still remain as a mixture when molten. Convection and settling certainly occur in the molten state. I believe that your initial conclusion concerning density might be correct. If this were a Pb-Sn-Sb alloy however, Sn and Sb are right next to each other on the periodic table, so separation only occurs from oxidation out of SOLUTION of Tin and Antimony. These two are still in a MIXTURE with the lead.
shoe
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/magazi...l89partial.pdf
Wayne
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 solution 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
uh huh - trapped air pocket(s) during casting. unloading a full ladle usually cures that, as mentioned before.Quote:
Originally Posted by texasmac