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Thread: cast boolit flaws due to shrinkage: announcing the solution (for me anyway).

  1. #1
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    JonB_in_Glencoe's Avatar
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    cast boolit flaws due to shrinkage: announcing the solution (for me anyway).

    Old photo, that I posted in cast pic of the month back in 2013.
    http://castboolits.gunloads.com/show...-Imperfections



    OK, I've been casting for 4 years.

    As like many of us newbies, I am continually seeking to improve my technique. One issue I have had, mostly with long rifle boolits, is shrinkage. A few different examples of such are shown above.

    I've asked questions about this, at least a couple times since I started casting. I've tried the suggested answers and while they may have been good ones, they weren't my solution.

    For me, this shrinkage issue was about as random as it gets. sometimes it seemed like it was one particular cavity of a mold...so I'd try changing the order that I'd pour the cavities, many times it helped, but the shrinkage issues would always return sooner or later.

    I tried different alloy formulations...more Tin, then Less Tin. Once in a while the problem seemed to get solved...only to show up in the next casting session ???

    I obviously tried different alloy temperatures and casting faster (to raise the mold temperature) as well as casting slower and using a fan to cast with a cooler mold and getting shiny boolits. It seems each time I'd make a change and go with it, the problem would go away...only to show up after I'd get into a rhythm ...as soon as I'd get comfortable, the shrinkage issues would pop up and get more frequent.

    I think I found the solution last summer. If you clicked on the link at the top of this post and scrolled down to #8 to see my March 2013 photo submission, you'll see I edited the text in August 2014 with what I figured out this summer.

    I wanted to make a grand post like this back then, but I thought I solved this problem so many times before, I was hesitant, for fear I was wrong again.

    So now with several successful rifle boolit casting sessions under my belt, I am comfortable announcing the solution to my problem.

    The Solution:
    Pouring as large of a sprue puddle as reasonably possible.

    My problem I had to overcome to resolve this:
    I'm sure I've read about pouring a large sprue and I'm sure I've been told that as well, when I asked about shrinkage in the past. But what it always came down to is...when I'd get into a comfortable pouring rhythm, I pour a smaller and smaller sprue...so as to reduce the amount of alloy usage per pour which should yield more boolits per pot of alloy. I needed to reprogram my brain. More perfect boolits per pot is better than just more boolits per pot.

    The Photo below showns my most recent casting session using the NOE 358009, these have not yet been sorted, you may see a couple flaws here and there. NOW, if I have poured small sprue puddles as I did a year ago, more than half would have to be culled.

    That mold WAS probably my most troublesome when it came to shrinkage...I suppose it's ratio of length to width, is the greatest of all of the boolits I cast, which would probably exacerbate shrinkage from a small sprue puddle.

    I just thought I'd share this, because it took me soooo long to figure it out, even though the solution was always close at hand.
    Good Luck,
    Jon

    ~~~~~~~~~~~~~~
    “If someone has a gun and is trying to kill you, it would be reasonable to shoot back with your own gun.”
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  2. #2
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    The faster ya go the be hinder ya get.
    This works for a lot of stuff I do, but never thought about it and casting.
    Thanks for the info, just helped me a lot.
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  3. #3
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    Bottom pour needs a large sprue for sure.
    I ladle cast and hold the ladle on long enough for the boolit to take all the lead it needs from molten lead so I can go with a small sprue.
    I am so glad you figured it out and you have a fine bunch now.

  4. #4
    Boolit Master

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    Once you find what works for a particular mold. Post it above your casting pot so you know for next time. I have some molds that like one thing or another for best results and keep a poster board with notes at my casting station. Temp, pace, pour method, all good things to write down for next time, especially if you use many molds.
    Every shot you get in life counts

  5. #5
    Boolit Grand Master popper's Avatar
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    IMHO, the idea behind a large sprue is to keep the sprue (reservoir) hot enough to flow into the cavity. Your lower left boolit is interesting because it appears the body is frosty & the base is NOT. Upper left is cold mould. Lower right has bad shank fillout but the rest looks good. I think you also get cleaner alloy as you learned. Too large a sprue will possibly stop proper venting. Maybe the better mould helped also.
    Whatever!

  6. #6
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    Quote Originally Posted by popper View Post
    IMHO, the idea behind a large sprue is to keep the sprue (reservoir) hot enough to flow into the cavity. Your lower left boolit is interesting because it appears the body is frosty & the base is NOT. Upper left is cold mould. Lower right has bad shank fillout but the rest looks good. I think you also get cleaner alloy as you learned. Too large a sprue will possibly stop proper venting. Maybe the better mould helped also.
    Popper,
    Are you implying that a Large, as possible, sprue puddle is not my solution to long rifle boolit shrinkage problem ?

    The photo was taken for a cast pic of the month contest...to show a variety of shrinkages... it was taken 18 months ago, I haven't photographed any other shrinkage issue boolits and that old photo with varied boolits doesn't necessarily convey commonality of the shrinkage I had. Although, I guess I can say the upper right boolit's shrinkage, at mid point (on the bore ride section just above, and including, the top driving band), is representative of the vast majority of the culls I experienced.

    BTW, mold quality didn't help...Maybe I didn't convey it clearly enough, The NOE 358009 mold was the worst offender of shrinkage...til I started pouring large as possible Sprue puddles.

    I am curious about your comments about cleaner alloy and "too large a sprue will possibly stop proper venting".
    How will either of those effect shrinkage ?
    and how will that stop proper venting ?

    Thanks for the input,
    Jon
    ~~~~~~~~~~~~~~
    “If someone has a gun and is trying to kill you, it would be reasonable to shoot back with your own gun.”
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  7. #7
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    I'm not convinced that a large sprue can interfere with venting, since it sits on top of the sprue plate. Venting occurs between the blocks, down along the length of the cavity, through the vent lines.
    Warning: I know Judo. If you force me to prove it I'll shoot you.

  8. #8
    Boolit Grand Master In Remembrance
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    Alloy fill out is simple: ladle pour > spout in sprue hole > 5 seconds pour > pot melt & mold same temperature so sprue puddle frosts in 5 seconds and keep a good rhythm. Has worked for me for many years with bullet weights in a 0.05gr Bell Curve. And I cast small and large bullets for long range BPCR shooting the same way
    Regards
    John

  9. #9
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    I always recommend as large a sprue as possible, when ladle casting I not only pour a large sprue I let it keep running right over the side of the mold back into the pot. I don't look at it as pouring lead but rather pouring heat. Can be the cure for several ills and go a long way to quality bullets.

    Since it's been since last summer that you've experienced the "shrinkage" I would say that your doing it just right.

    Rick
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  10. #10
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    I knew Rick would throw the ladle in there. I got one after he nagged me like an old woman, he was right.

    I don't pour large sprues but I do pour lots from the ladle for a few seconds after each cavity is full. Lots of heat makes a difference.
    You will learn far more at the casting, loading, and shooting bench than you ever will at a computer bench.

  11. #11
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    Allow me to post a little experiment i did yesterday while casting. I had about 17 lbs. of 92-4-4 alloy made from certified metals, and I am (was) a firm believer in the superiority of ladle casting. I knew, however, that after about 250 bullets or so, the large Rowell ladle would not be able to scoop up sufficient alloy from the Lee pot, and I planned to switch to bottom pour.
    My plan was then to cull and weight sort the bullets from the 2 sessions and compare the 2 bell curves to determine which casting method was the better.

    First casting setup:
    Click image for larger version. 

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    Second setup:
    Click image for larger version. 

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    Now I was convinced that the ladle poured bullets would be more consistent, since the ladle gets a larger, stronger stream of lead into the cavities in a shorter period of time. This did not happen.

    Ladle poured bullets:
    Click image for larger version. 

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    Not exactly a bell curve to brag about.

    Bottom poured bullets:
    Click image for larger version. 

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    Disclosure: I have opened the pour spout on my Drip-O-Matic from 1/16 to 3/32 to get a stronger stream of lead.

    OK, so I thought that I had discovered something great here, like an "Earth-is-round" thing.

    HOWEVER, the more I thought about it, the more one thing started sticking out in my mind:
    When ladle pouring with my HEAVY brass 4-banger mould I would rest the mould on the edge of the pot while pouring.

    What does that have to do with anything? It angles the mould down (if I didn't angle the mould into the pot the 2-lbs. Rowell ladle would pour lead everywhere), and there was never a consistent SPRUE on the sprue plate. Pouring with the Lee B.P. on the other hand, as you can see in the picture, a healthy sprue was poured every time, making for a more consistent quality. Cull ratio (visual defects) was the same for both pours, right on 10%.

    So, in conclusion there is no conclusion. My 2 pouring sessions showed what 2 different techniques will produce, but it wasn't apples to apples.
    Goodsteel is lending me his 2-cav NOE XCB mould so I can repeat the test with the mould fully hanging inside the rim of the pot so I can leave a sprue while pouring with the ladle. We shall see.
    Attached Thumbnails Attached Thumbnails IMG_2574.jpg   IMG_2575.jpg  

  12. #12
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    The smaller pot would make it more difficult. I recommended the Rowell #2 to btroj & I think he uses an RCBS pot. A month or so ago I was at winelovers place and did some casting with my Rowell #2 and his RCBS pot & got a good reminder, the smaller pot took some getting used to. Made me appreciate my Magma though.

    I think the healthier sprue is a benefit, been recommending it for a long time, some listen some don't.

    Rick
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  13. #13
    Boolit Grand Master
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    I am seriously considering a Magma 40 pounder. I have a #2 Rowell, I listened Rick, and it is awesome.
    I did learn that pouring into the cavity for a period after it is full makes a difference. The base quality suffers if I fill and move on. Fill, keep pouring, then move to the next cavity.
    You will learn far more at the casting, loading, and shooting bench than you ever will at a computer bench.

  14. #14
    Boolit Master
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    Yep..........sprue plate is too cool and the drive bands don't fill out before the alloy near the sprue plate (base of the boolit) solidifies. A mold that doesn't vent well makes this situation even worse.

  15. #15
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    A large sprue puddle creates pressure to fill the cavity, and more hot lead toward the center. What I dont understand is why sprue plates are so darn thin on deep molds. Common parts is a great idea, when they work. But, deep molds need higher pressure. So do smaller diameter molds. What's so wrong with a thicker sprue plate to increase pressure? I drill mine out to increase flow rate, which helps, but cutting the sprue is then harder as well. It frustrates me that mold builders do not address this basic issue we learned in high school casting, like 40 years ago. Molds that do not work does NOT help their business.

  16. #16
    Boolit Master 35 shooter's Avatar
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    JonB Thanks! This was a timely post for me as i realized i've been doing this very thing lately...as in pouring a smaller sprue. Today i kept the sprues thick and had no rejects as far as fill out. I just thought the lack of fill out was just the mould getting too hot, but evidentally not, as i had no problems today. This was a good reminder for me...Thanks again!

  17. #17
    Boolit Grand Master



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    Quote Originally Posted by stephen m weiss View Post
    What's so wrong with a thicker sprue plate to increase pressure? I drill mine out to increase flow rate, which helps, but cutting the sprue is then harder as well. It frustrates me that mold builders do not address this basic issue
    Do have any NOE or MP molds?

    Rick
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  18. #18
    Boolit Master


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    Try this experiment.

    Pour a very small sprue. Only enough to fill the vent. not enough to make a puddle.
    Watch what happens.

    You will actually see the lead from the small sprue flowing into the mold through the hole.

    In some cases, the flow into the mold will leave a small hole in the sprue and when you cut it off, the hole will continue into the base of the bullet. Alloy will absolutely flow into the mold from the sprue. IF: the metal hot enough to flow as the bullet shrinks.
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  19. #19
    Boolit Master Jack Stanley's Avatar
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    Thanks Jon , that explains why my LBT moulds don't have that problem and some of my other moulds do .

    Jack
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  20. #20
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    As you've found, pouring a large spru is important for fill out, but looking at the voids on the
    2 boolits on the left and center, makes me believe they are air pockets, not a spru size
    problem per-say.
    If you will notice that all the voids are no where near the parting lines meaning that the air
    was trapped and could not get out.
    I have always poured a large spru but on occasion have had the voids shown in your photo,
    my cure was to watch what side of the mold it happened on and tilt the mold slightly
    in that direction to help remove the air.
    Calamity Jake

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check