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Thread: MP 8 cav aluminum mold alignment pin issue

  1. #1
    Boolit Master
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    MP 8 cav aluminum mold alignment pin issue

    I've never had an alignment pin move, and don't remember hearing about it happening in an MP mold, but I think that's the problem I have been dealing with.

    I started using a new 9mm mold from Miha. Perfect on inspection right out of the box and after initial mold prep. Great casts in the first two or three sessions, but then persistent finning and feathering started to appear, along with visible parting line defects, almost always from the boolits dropped from the far end of the mold.

    A close look showed visible light between the closed blocks, wedge shaped, with contact only at the near end, a widening gap at the far end, with the only other contact at the far alignment pin. The male pin was proud, and the female pin nearly so, or at least not as inset as the other female pin. I pressed the blocks together with a hydraulic shop press (hugs from a vise and love taps with a hammer didn't budge the pins at all), applying pressure just over the affected pin set, with lead ingots protecting the blocks themselves, and the mold is back to dropping great boolits.

    The only thing I can think of as a cause is that the mold got very hot on preheating prior to the problem appearing. I'd built an insulated mold garage that works too well: what used to need at near max setting with molds sitting a long time directly on the coils to get to casting temp (205° C, or 400° F, measured with a K probe set in one of the cavities) now takes a medium low setting and much less time, even with an aluminum pad between the blocks and coil. A buddy I'm showing how to cast started preheating while I was away doing something else, saw the temp reading rise to around 200°, and let it go up, mistaking Celsius for Fahrenheit. He got sidetracked, and I came back to find the probe reading 450° C (~840° F), and for an unknown time.

    All seems OK for now. I've read here that Lee doesn't recommend letting their aluminum molds staying over 450° F for long because there can weakening or warping of the blocks. MP molds are a different alloy, I think. Anybody know for sure?

  2. #2
    Boolit Master
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    I wish I had a way to quickly check mold temperature. I wonder just how reliable those infrared guns are. I have a brass four cav MP .44 hp mold and it does like a hot preheat. Seems to hold temp pretty well with my alloy at 700. With an 8 cav and those long blocks any warpage would certainly cause problems. I would give a real close inspection to make sure there was no specks of lead on the mold faces.

  3. #3
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    Mal Paso's Avatar
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    It was a common problem and I thought Miha was cross pinning the alignment pins now. That's what I did.
    Attached Thumbnails Attached Thumbnails MoldPin0.jpg   MoldPin1.jpg   MoldPin3.jpg   MoldPin2.jpg  
    Mal

    Mal Paso means Bad Pass, just so you know.

  4. #4
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    Quote Originally Posted by Cosmic_Charlie View Post
    I wish I had a way to quickly check mold temperature. I wonder just how reliable those infrared guns are. I have a brass four cav MP .44 hp mold and it does like a hot preheat. Seems to hold temp pretty well with my alloy at 700. With an 8 cav and those long blocks any warpage would certainly cause problems. I would give a real close inspection to make sure there was no specks of lead on the mold faces.
    Infrared guns are not any good with shiny metal.
    Mal

    Mal Paso means Bad Pass, just so you know.

  5. #5
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    K type thermocouples are pretty cheap, as are multimeters, if you don't already have one lying around. I just pop the bead end into one of the cavities.

    Yeah, I originally thought the problem was lead on the mold faces, but didn't find any, and between the normal near end and the far pins the only place there was no visible light (contact) was at the mated pins themselves.

    I guess it's possible that the problem was warped blocks that the press straightened out, but I'd checked the blocks back to back and side to side and didn't see light between them, and the ram on the press was only applied at one end of the blocks, over the problematic pin set.

    Well, the gap is gone and the casts look good. My main concern is if the mold has been annealed to the point of softening the blocks, and whether that'll effect its useful life. I have an email in to Miha, but, really, only use over time will tell. If the main problem will be just the pins shifting, I can try pinning them (thanks, Mal, for the detailed How-To in another thread).
    Last edited by kevin c; 09-22-2021 at 02:34 PM.

  6. #6
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    Mal Paso's Avatar
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    Aluminum expands faster than steel and I think the pins get lose at the upper end of casting temperature and for me, tapping the hinge pin provided the energy to move them. I only have one aluminum MP mold, a #503 and it's rare that all the boolits fall without help, it's a Keith thing. I was well into the pot when the finning started so it can't be all a preheat problem.

    If you look at the note from Miha the problem there was pins receding but I think it's the same problem, not enough grip on the pins at elevated temperatures.
    Mal

    Mal Paso means Bad Pass, just so you know.

  7. #7
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    Something I've been meaning to do is to get a computer fan I can set up in my casting area. I've read here that people use them to help regulate mold temp. You just hold the opened mold in the breeze for a bit between fills. Even running my pot at 680 my mold over heats fairly quickly. But when the temp is right it drops shiny crisp hollow points. I may also try a 2.5/2.5/95 alloy, a bit bit harder than I've been using but it should shrink more aiding in release.

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