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Thread: Bottom pour techniques

  1. #1
    Boolit Mold
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    Bottom pour techniques

    A week ago while browsing around the local reloading mercantile I found an NIB Lyman Mag 20. Today I finally had time to melt some lead. The technique that worked best was to press the spout into the sprue plate recess. I thought the correct way to do it would be to position the mould on the rest and pour a stream into the recess. But no matter how I tried, the lead would cool on the sprue plate and not fill the cavity. I believe next time I’ll set the mould upside down on a hot plate and see what that does. What technique works for you folks?

  2. #2
    Boolit Master 15meter's Avatar
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    I have an air gap, but I pre-heat the mold on a hot plate. I tried the "pressure cast" method with the sprue plate against the nozzle, never got the hang of it.

    The mold is definitely not hot enough and perhaps the lead is on the cool side.

    What's your alloy? Do you have enough tin for good mold fill out?

    Also, vary the flow rate, you may have too little alloy entering the mold and it cools too fast.
    Last edited by 15meter; 10-13-2020 at 11:15 PM.

  3. #3
    Boolit Buddy gnappi's Avatar
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    Sounds like your alloy isn't hot enough, and your molds are too cool crank it up.
    Regards,

    Gary

  4. #4
    Boolit Buddy
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    I heat my molds to 350 on a hot plate, heat the sprue plate on each side with a butane torch for about 10 seconds on each side and I run my alloy in the pot between 700-750 degrees. Make sure you have a thermometer in your pot when casting to make sure you maintain a steady temp.

  5. #5
    Boolit Buddy
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    I preheat my mold, just so I don't have as many rejects to start. I don't touch the spout, instead dropping the stream into the mold. If I "pressure" cast I get spout clogging and voids in the base of the bullets. Remember, the column of lead determines the amount of pressure. A sprue puddle will have very little difference in pressure. At first I run a large puddle of lead on the sprue plate to heat the plate up well. Usually I just keep pouring and move the mold to the next cavity. That way I only have one sprue. Later, as the sprue plate comes up to temp, I reduce that puddle size. Sounds like you need to raise the temp of both your lead and mold. I run hot and fast until the bullets start getting frosty. Then slow down a little.

  6. #6
    Boolit Bub monkey wrangler's Avatar
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    Somehow I got the only lee 4-20 pot that does not leak so mine starts to build up in the nozzle then the flow gets slower. That is when I have problems with mold fill out. I would try faster flow as well check your temperature like the other guys are saying.
    Life is tough, but it's tougher when you're stupid. John Wayne


  7. #7
    Boolit Master
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    some molds like to have the lead swirl around the sprue plate some like pressure cast,you need to get the mold and lead hotter.

  8. #8
    Boolit Grand Master

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    I preheat my mold on a hot plate but I don't know what temperature I get it up to. I never paid it any attention. About the middle of the temperature knob. I usually get good bullets about the 2nd or 3rd pour. And I have a gap between the spout on the pot. Again, I don't know how big of a gap but its large enough that I can see the top of the mold. Probably 3/4 to 1 inch. I tilt the back of the mold up slightly and start pouring into the cavity away from me working toward me.

    Everyone has their own technique so just develop one thats comfortable for you and that works.

  9. #9
    Boolit Mold
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    Thanks guys, I'll try hotter and faster. monkey wrangler, from what I've read that Lee pot isn't working correctly. You ought to tweak it until it starts dripping. By the way, if any of you folks are near Nashville, The Reloader's Bench in Mt. Juliet had another of those Lyman Mag 20's a week or so ago.

  10. #10
    Boolit Master
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    Another factor affecting cooling of the mold, sprue plate and the poured alloy is environmental temperature. Casting out of doors, I find that lower air temps and windy conditions need countermeasures of higher alloy temps, faster pours with more volume in the alloy stream, a quicker cadence, a shorter alloy drop to the mold, a bigger sprue puddle, or some combination of the above.

  11. #11
    Boolit Master
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    Start by pre heating the mold and setting the lead temp too hot. This will help get everything up to good casting temp and beyond fairly soon. Then when boolits start coming out frosty back the temp down until they are just slightly frosty and make a big pile of just slightly frosty good boolits.

  12. #12
    Boolit Master
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    Second the slight frosting on the boolits. That's the sweet spot I'm going for with all the different tweaks; when I see that slight matte appearance, I know from experience that the mold is dropping all nigh on perfect keepers (95-3-2 alloy).

  13. #13
    Boolit Buddy
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    by pressure pouring ex putting the spout on the hole and pouring I feel you are keeping the sprue plate too cool. I use a bottom pour pot as well as a ladle at times. In each technique I make sure I have about a dime size sprue on each hole. I find the extra lead of the sprue keeps the sprue plate hot and at least up to mold temp or close.

    I also keep my alloy ( typically COWW or ISO core) between 675 - 725 . I also dip the edge of my mold into the lead and let it preheat. Even with my six cavity aluminum mold I am typically casting good bullets on the second pour.

  14. #14
    Boolit Buddy
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    Mostly you need: hot enough, air gap, nice puddle. But I do have a couple molds that think they've gotta' have contact. Whatever it takes.

  15. #15
    Boolit Mold
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    I forgot to mention that a couple of my moulds are Saeco which have tiny holes in the sprue plate. I opened one of the holes and it helped.

  16. #16
    AKA: GRMPS Conditor22's Avatar
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    welcome to CB faraim

    I open and sharpen many sprue plate holes

    rule 1 take the sprue plate off the mold
    rule 2 get a 200-400 grit sheet of wet/dry sandpaper, set it on a piece of glass or tile (something perfectly flat) and smooth the bottom of the sprue plate before reassembling.

    smaller holes make it more difficult to pour but give nicer bases

    many sprue plate pour holes aren't countersunk far enough and have a flat area that makes it harder to cut the sprue and tends to tear/pull the lead
    Polish the holes when your done, it helps with flow and sprue release

    I occasionally pressure pour (hold the mold up to the spout) to check fillout and warm the mold a little

    preheating the mold to 400 on a hotplate with a piece of metal/sawblade on it really helps, many of my molds will drop perfect boolits on the first cast.

    I also cast between 690-720 (except pure need 750) the harder the alloy the lower the melting point

    I generally adjust my mold guide to have the top of the mold 1/2 inch below the spout, have the spout lined up with the sprue holes and pour this way most of the time

    as previously asked -- what alloy were you using?

    did you smelt the lead and flux it multiple times with both sawdust and wax?

    you don't want to put dirty lead in your pot it will plug your spout (I smelt all the lead I get) lead is heavier than anything you put in your pot but stuff still gets to the bottom of the pot and plugs the spout ------ haven't figured that one out yet

    did you flux the lead in the pot before you started casting.?

    how cold is it where your casting?

    if you let the spout get cold the flow will slow and the spout can plug up I have a propane self igniting torch by my casting setup for when that happens

    you don't need to turn your mold upsidedown on the hotplate, it will heat up given time (I usually turn on the pot and hotplate at the same time so my mold(s) haet up when the lead is melting.

  17. #17
    Boolit Mold
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    Thanks for the tips. I was using 16-1 alloy from Rotometals. I didn't flux it, but have walnut shavings/sawdust and wax standing by for the next adventure. The outside temperature was in the low 70's and my lead was between 650 and 700 degrees. The only time my spout plugged was when I was adding more lead, although since I was holding the mould up to the spout, I really don't know about the flow. Getting all of this great information is the best welcome to the forum anyone could get! Thanks.

  18. #18
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    Conditor, I figure that gunk getting below the lead is that Murphy feller, he is good at messin' things up!

  19. #19
    Boolit Master
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    I always preheat my molds on a hotplate with a half inch thick round aluminum plate on it & heat the mold to 350 to 400 degrees using a temp probe in the mold. My lead temp is usually kept at 750 to 775 degrees. I fill from back to front with about a 3/8 gap. Use as fast a flow rate as you can without making a big mess. One thing I have yet to see mentioned is you must adjust your flow rate slightly as lead level lowers & the pressure head decreases. The ProMelt makes it easy to do this. I also make my sprues as large as possible to keep the sprue plate as hot as possible. Angleing the mold a little while filling to get a slight swirl is also helpful. I have often thought having a small ridge around the edge of the sprue plate would be helpful. If I could weld, I would try it & then flatten the bottom again on a granite surface plate.

    Bob
    Si hostes visibilis, etiam tu

  20. #20
    Boolit Master
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    to pre heat my molds i just fill them and let them sit for a couple of minutes ,dump the boolits then refill mold it should be ready to go.

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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