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Thread: Help: Void issue with new alloy

  1. #1
    Boolit Master
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    Help: Void issue with new alloy

    Last fall I made a new batch of alloy. About 400 lbs or so. While I was working out of state the other Mainiacs foolishly allowed the state to outlaw lead wheel weights so this batch was something I made using pure lead from phone company splice boxes, old plumbing and flashing scraps, combined with antimony powder bought on this site and some pewter accumulated over the years, filled out with about 200 lbs of smelted down window sash weights from a 200 yr old home I tore down at work. By my primitive calculations I should have been somewhere around 95/3/2. The issue is a problem I haven't seen before: Voids at, (under) the sprue. I was using molds I've had for years, #68 H&G and 230 BDACP for 160 lbs or so,(several hundred thousand boolits cast in them previously), with the exception of a new 147 grain 9mm mold, (maybe 20 lbs cast). Same Master Caster I've used for years, same temp, same technique and timing, boolits and sprues appeared completely normal while casting, although maybe not as much visible shrinkage on the sprues down into the mold, (This is a little hard to judge on a master caster as you don't get a good eye on it until you move the mold out from under the spouts.) The voids are more or less centered in the base under the sprue. Larger and more obvious on the 45's, smaller and less obvious on the 9mms. The boolits all look great, except for the 5% that show some level of void at the sprue. The rest of them weigh as consistently as usual, so I don't think this is random voids. I'm thinking this has to be an alloy issue involved with the fill/cooling at the sprue?
    5% is not a huge issue, it's just one more thing I have to look at individually which is a PITA when working in bulk.
    Any opinions on this? I have another 400 lbs or so of this material and I'd like to get a clue before making more alloy.

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  2. #2
    Boolit Master

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    Seems to me you are cutting the spru before the melt has sufficiently hardened, which pulls out a "plug" from the base. Slow down a little. Also, show us a profile of those boolits...please.

    Quote Originally Posted by https://www.americanrifleman.org/content/bullet-casting-from-ingot-to-bullet/
    Also, make sure you give the lead enough time to fully solidify before knocking off the sprue and dumping the bullet. If you see a significant tear on the base of the bullet or a smear of lead across the top of the mould, you are going too fast.
    Last edited by Land Owner; 04-19-2023 at 08:05 PM.
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  3. #3
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    Looks to me like the lead, mold, or sprue plate was not hot enough. Might want to add some tin if you have solder or pewter.

  4. #4
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    Raise the heat until they start to frost.
    Back it off some, and let your puddle sit & cool a few seconds longer.
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  5. #5
    Boolit Master
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    Boolits are nice and somewhat frosty on the lower two thirds. I am definitely not cutting the sprue too early as I'm certain that I would see some lead smear on the top of the blocks if I was. I am not a newby at this. I'm using the same 6 second cycle on the master caster that I've used for the last 150,000 boolits that I've cast using this machine and these molds. I'll post picks of the boolits tomorrow. There is no difference that I can see in the outward appearance of the 95% which are good, and the 5% which have the void at the sprue. I cast the 3,000 +/- #68s in two afternoons, and the 1,500 BDacps in one session. The boolits with the voids under the sprue seem to be pretty evenly mixed through the pile, so it's not like they were all cast at the beginning of the session, or all near the end. The only variable seems to be the alloy.

  6. #6
    Boolit Master
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    Considering the amount of alloy you made and the sources of lead used you might want to send off a sample to BNE to have it analyzed and then you know for sure what you are working with. Right now you have no idea what was in the window sash weights and you added antimony powder without knowing the antimony content of the alloy you were adding to. That is where I would start, find out what you actually have so you aren't just chasing your tail.

  7. #7
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    If you don't have one, I'd encourage getting one or downloading a older edition.
    There is a section in the front end that goes in depth about this problem, and others you might run into.


    Actually, the shrink holes aren't really that big of a deal if you're just loading practice handgun ammo.
    Weigh some and see what percentage that they are lighter than a fully filled one.
    If it's only 1-3-ish percent, I'd load & shoot 'em.

    I'm a lot mot particular for rifle ammo, but for handguns they should do OK.
    Last edited by Winger Ed.; 04-20-2023 at 01:13 AM.
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  8. #8
    Boolit Master
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    I did not catch in what batch size(pounds) you cast your projectiles, but I would melt a "half-batch" of your alloy, and try adding 1/2% more of its weight pure tin, mixing thoroughly, and casting as you usually do. If the voids do not disappear, add another 1/2% of the total batch weight.
    While I have no reason to distrust your calculations, let's PRETEND that your actual tin content is one-half what you think it is. With 1.5% Sn, I would expect that you would find voids not only in the base, but also on the driving bands and maybe even the nose of the cast bullets. If you add pure tin in the amount I describe, it will raise tin content by slightly less than 0.5% and maybe get it close enough to 2% minimum (if not already there), to give better fill-out and abate voiding. If you still get voiding at the base, adding additional tin in the same amount will elevate total tin content by just under 1%, to a theoretical ~2.5% Sn, which ought to fix the problem.
    If the voiding is not resolved after a second addition of tin, then I'd be far less confident that low tin content is the culprit, but a third addition of pure tin in the same amounts as the first two might prove to be "the charm". If more tin fixes it, just keep track of the proportion in which is was added, as you scale up.
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  9. #9
    Boolit Master
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    The only problem I see with doing that is what if it doesn't work? Then you now have another unknown alloy you are looking at. And you have wasted expensive tin. That is why I say have it tested to see exactly what you have so you KNOW where to go. Not Guess where to go.

  10. #10
    Boolit Master
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    I've attached a picture of the boolits involved. I don't think the profiles have anything to do with this issue as they are varied. They test right at the same hardness as WW using my cabin tree tester, (.080), and there are no apparent voids anywhere else. The only voids appear to be right under the sprue on these 5% of the boolits dropped. I make alloy in 200 lb batches, The master caster has a 40lb pot, which I try and keep at 80% full or more while casting by adding 3 lb muffins one at a time which have been preheating on the rim of the pot. The majority of what I cast are for practice and action pistol matches. So I'm sorting out the ones with the voids at the sprue. The other 95% seem fine, no evidence of voids, weight is +/- less than a grain. It's just a pain to sort out the ones with the voids. In the past once the mold was warmed up I had no rejects unless something came loose on the machine, or I bobbed the pour lever.Click image for larger version. 

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  11. #11
    Boolit Master
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    Thanks for the help. I have two questions:
    Winger Ed, what is it that you're suggesting that I read? It's possible I have it, a lot of books on the shelf here.
    And, where would I send a sample to get analyzed?

  12. #12
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    It almost looks like maybe you didn't get good flow in the last half on the poor. But not necessarily from a tin issue, but maybe a heat issue. I would try two things, first off you don't mention what temp your pot is at. I'd try raising it to 700-750*. If you're already at/above that mark, you might try speeding up the casting. The reason I say this, if you're not casting fast enough maybe the molds are not staying hot enough. It's really hard to say, as the pictures are small and you can't really zoom in much. Maybe post some close-ups of the boolits in question....
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  13. #13
    Boolit Master TurnipEaterDown's Avatar
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    The pictures are pretty small.
    Do I see rounded base edges on some of the pictured bullets?

    Voids under sprue columns: Voids here are often caused by insufficient sprue volume fluidity as the bullet core is cooling and shrinking. The bullet needs to draw new metal in as the solidification process continues to prevent voids. Voids at the sprue connection would likely be from too quick of bullet cooling, or insufficient sprue temperature and fluidity during solidification.

    I used to manage issues from design, manufacturing, etc., and one of the things that always made me cringe was '...nothing has changed...'. Something most often has changed if performance of a reliable operating system has changed. Trick is: what?

    What is the ambient temperature in the bullet making space compared to last time you were successful? Is there a fan running in that room, when there wasn't before, etc. These things could impact cooling rate of the bullet in the mold, or the temperature and thus fluidity of the sprue.
    Did the alloy composition change, affecting fluidity, or other casting/solidification characteristics? Statement is made about the gross lead/antimony/tin %, which I will just take as best honest truth, but even trace levels of some contaminants can lead to fluidity issues.

    Maybe figuring out the factual cause would be too much effort / expense, so the remedy might just be to drive a higher temperature at the sprue puddle. Higher sprue plate temp might be the best goal, as raising the resevoir temp may just make for more draw from the sprue being required as the bullet cools and if the sprue itself is cooling faster than the bullet it would not help.

  14. #14
    Boolit Master
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    As I said, this is a new alloy. Everything else has stayed the same, (except the 9mm mold which is new). Prior to this my alloy was about 90% WW with a little of whatever else came my way. My pot is set to 750 degrees, I cast in my shop, (heated by a wood stove) mostly during the winter so the area under the hood where the master caster is set up starts around 60 or so and gets warmer as I keep casting. It appears that I have this issue both early in the session, (after the first hundred boolits which I always dump back in the pot), and near the end of the session, (after 1,000 boolits have been cast). Hard to imagine that after 500-600 cycles at 750 the mold would be too cool. Flow from both spouts is generally good, The flow from a master caster is several times faster than the flow from my Lyman 20lb pot. It takes less than a second to fill the cavities, then I leave the mold under the pot until the "Three count", at which point the sprue is starting to "dull" as it solidifies, than I pull the handle down halfway exposing the sprue to the two cooling fans for another 2 seconds than dump the boolits at the "six count". I might need to clear a spout once or twice every 2,000 cycles or so. The master caster uses a two cavity mold which I cycle every 6 seconds, so about 10 cycles a minute. If I try and go faster than that I typically have trouble with lead smearing between the top of the mold blocks and the bottom of the sprue plate. The H&G #68 mold is a bevel base, and those are the boolits in the picture of the cavities, as those were the boolits I was sizing when I picked up on this issue. Fill out seems to be very good with the exception of the 5% that have these voids under the sprue. I did add granular antimony by pre-melting it in some lead/tin solder before I added the rest of the lead to the melt. I heated it up to 700 and fluxed it. It appears to be fully dissolved at that point? Maybe it should have been hotter?
    I have thought about the possibility that some little chuck of antimony occasional blocks the hole in the sprue, but if that were the case you'd think I'd see some partial boolits as the chances of the blockage always occurring at exactly the same point in the pour seem pretty slim.
    Last edited by BD; 04-21-2023 at 04:24 PM.

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    Boolit Master
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    I did shoot a couple hundred of the #68s today, (I had sorted out the ones with the voids at the sprue), and they shot fine. 3" at 25 yards on paper from the bench, and I was ringing the steel reliably. I'm no bullseye shooter, that's for sure. But I don't see any issue with the ones that don't show the voids. I shot twenty rounds at 10 yards over the crony to check my new lot of Titegroup, and those went into an inch and a half.

  16. #16
    Boolit Master TurnipEaterDown's Avatar
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    Not being picky, but voids at the sprue on the occasional bullet might be circumstantial.
    Have you taken a sample (say 50) good looking ones, and weighed them to look at the distribution and compare to the weight of ones with obvious small voids at the sprue cut? Are the ones with obvious voids really unique outliers?
    It should help sort out if this is a random occurrance (occasional void at sprue) that you can then hone in on for cause, or determine if it is an indication of another particular problem (such as voids in general occurring).

    Really seems like your alloy change could be a likely cause, but I have seen a number of times that the obvious thing isn't the cause, and that's where my earlier comments were aimed: when unsure, look at physical causes for the observed fault and rule in/out each potential cause by investigation. Of course it is helpful to start with your best educated guess. Some people use an IS/Is Not assessment to find problem causes. There are a number of root cause analysis tools: fishbone (ishikawa diagram I think is another name, and I could be spelling that wrong), pareto charts, 5 why methodology, etc.

  17. #17
    Boolit Master
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    Since you changed molds, are there physical differences in the mass of the present blocks and the ones you used before. Perhaps a different mold maker used a different metal alloy? May as well verify that the sprue holes in the sprue plates are the same while you are at it.

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    Quote Originally Posted by Winger Ed. View Post
    Raise the heat until they start to frost.
    Back it off some, and let your puddle sit & cool a few seconds longer.
    This is the first thing I do when something is not right. Make sure the lead has been adequately fluxed. Slowing down when cutting the sprue could help. Weighing the boolits to see if there’s a difference between them, can let you know if there are voids inside.

  19. #19
    Boolit Master
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    [QUOTE=TurnipEaterDown;5567791]Not being picky, but voids at the sprue on the occasional bullet might be circumstantial.
    Have you taken a sample (say 50) good looking ones, and weighed them to look at the distribution and compare to the weight of ones with obvious small voids at the sprue cut? Are the ones with obvious voids really unique outliers?
    It should help sort out if this is a random occurrance (occasional void at sprue) that you can then hone in on for cause, or determine if it is an indication of another particular problem (such as voids in general occurring).

    As I mentioned above, the boolits that do bot show the obvious voids weigh out in the typical distribution I have always experienced with this machine, +/- <1%. The master caster is a very consistent way to cast. All of these molds are iron, and while they are from three different manufacturers, master cast blocks are all the same size as they have to fit the machine. The only significant difference is mass is due to the differences in bullet design. Obviously a 147 grain 9mm mold has a smaller cavort than a 230 grain .45 mold.
    I am coming to think it is most likely an issue with the composition of the alloy. For whatever reason, the connection between the lead in the mold, and the lead in the sprue seems more tenuous than with the WW alloy resulting in 5% of cases where lead from the sprue is not sufficiently drawn down into the mold as the casting begins to cool.
    I may raise this question in the Master Caster sub-forum to see if anyone else has experienced it.

  20. #20
    Boolit Master TurnipEaterDown's Avatar
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    It could be the alloy change. Perhaps even likely is, by the description of event. But what you want seems to be a useful suggestion as to what do you do to "fix" the voiding.

    In problem solving, a person always should focus on the governing characteristics which generate the issue:
    To get the small base void, the lead in the sprue must be unable to donate metal effectively during the last stages of bullet solidification.
    The sprue is likely still in the liquid w/ solid solution phase but too close to being fully solid to ensure sufficient flow, or the join between the bullet base and the sprue puddle at the plate orifice is possibly fully solidified, before the bullet in the mold solidifies. As the bullet can not effectively draw metal from the sprue, a void is formed at the base.

    You relay that this voiding happens in a small amount of your production.
    So, either the process as it stands now is sensitive to small process changes, and / or small changes in boundary conditions.


    In looking at lead alloy phase diagrams, a person can see that small % alloy constituent changes can change the temperature point of the fully liquid to liquid - solid solution phase transition line, or the liquid - solid solution boundary line to pure solid, by a significant degree. To some this might suggest that feedstock is inconsistent, BUT by looking at these same diagrams with a different viewpoint it is seen that small temperature changes can have a significant effect on phases encountered, and % of those phases.

    So: if there is a significance to your alloy change, you can't leave all your settings / processes the same and expect the same results.
    You either would need to (a) change your alloy back to be compatible with your prior successful process settings, or (b) change some process steps or settings such as those which will affect the ability of the bullet to draw metal from the sprue at solidification.

    As stated, you can not get voids as you describe w/o having the bullet complete solidification after the sprue no longer becomes an effective sacrificial element for metal supply.

    I think in regards to sprue puddle function, a key statement in your process description is:
    "It takes less than a second to fill the cavities, then I leave the mold under the pot until the "Three count", at which point the sprue is starting to "dull" as it solidifies, than I pull the handle down halfway exposing the sprue to the two cooling fans for another 2 seconds than dump the boolits at the "six count"." And your statement "...the lead in the sprue seems more tenuous..."

    Prime option in my mind: Leave the mold "up" a little longer to increase the time when the sprue is likely still somewhat fluid under the outer skin that you see, before the cooling fans blow on it rendering it completely solidified and unable to donate metal.
    Your comment "the lead in the sprue seems more tenuous" also could be interpreted to indicate that the short column of lead alloy that is at the sprue orifice is donating metal both to the bullet and sprue puddle when the fans start to blow on the sprue puddle after lowering the mold, and the tenuous nature of the sprue is indication that it is rife with voids itself. IF the area of sprue at the orifice is solidified last, it could become crumbly, brittle, more like a porous construct because it is giving away metal to both sides of the interface. That orifice segment needs to be able to flow to draw from the puddle (even if mushy material is available) to assure complete formation of the bullet. Ideally, the bullet solidifies first, the sprue orifice / column next and then the puddle. It is a tiny cross section that could potentially cool rapidly enough (in terms of phase change), by the fan now blowing on the sprue / sprue plate, messing with that sequence and to stopping flow at the orifice.


    Other "fix it" options might be: Increase the heat dissipation of the mold (Lower the temperature of your molds/room temp, or introduce/increase airflow across the mold), find a way to increase the overall per-cast volume dispensed to provide an increase in material overflow after the mold is full to ensure a hotter/more fluid sprue as the bullet completes solification, add tin to (hopefully) drop the liquid+solid solution to Solid boundary line in the phase diagram to a lower temperature so that your sprue continues to feed the bullet longer during solidifcation, or perhaps increase the pot temperature to Hopefully increase the temp of the sprue as the bullet is solidifying (seems like it could be counterproductive: hotter material will create longer time to solidifcation in the mold).
    Last edited by TurnipEaterDown; 04-23-2023 at 09:32 AM.

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