I bought a new double cavity Lyman #358429 mould a year ago, right from the factory. I tried loading with it a few times but I ended up having other things come up and I forgot about it. The last few days I started casting with it again and for some reason it will not cast good bullets, or even bad ones. No matter what I try, perfect lead temp of about 750-800 degrees using wheel weights, letting the mould warm up right, it seems like I cannot get the lead into the mould fast enough before it hardens. I end up most times with 1/2 to 3/4 of a bullet even after an hour of casting keeping the temp to around 800 and when I do get a really good poor I have to go very slowly and pour just right to get a bullet, good or otherwise. Compared to this mould my little 358156 HP single cavity runs circles around it, I can get 100 bullets in the same time as I get 25 from this double cavity. Like I said it seems the lead is pooling on top of the plate and not getting into the mould cavities themselves. Can these be opened up and who does it, if that is even the problem.

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Vaya con Dios

Modifications are a last resort. you can always make a hole larger, sure, but you can't make a too large hole smaller.
Try to aim the lead steam just to the side of the hole and let it cascade into the cavity. If this improves matters some, but not enough, pour at the edge of the hole. You can also try starting the pour with the mold held at an angle and rotate to flat as it fills.
I have this mold in a hollow point version. yeah its a little quirky but I do manage with it.

If all else fails, and your afraid of taking a tool to it, drop me a line and we'll make some arrangements to sort it out.

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it just needs more voltage

I have the RCBS/Lachmiller clone of that mould. To get mine to fill, I hold it at a slight angle and pour to the side so the alloy swirls as it fills the cavity. I also have to preheat mine a good bit. Before I start I place the mould in the pot and leave it until its hot. The bullets start out frosty, but by finding the right rhythm the mould soon produces shiny well filled bullets. The trick with this mould seems to be, use a lot of heat at first. Get a good swirl when filling it, and take your time between pours.

David
Check the inside surfaces of the mold around the cavities. Make sure the mold has vent grooves and that they are clean and run to the edge.
Also, how do you heat the mold. Do you have a hotplate or? Mold temp and/or venting sounds like your issue. My 357429 pops out bullets like popcorn.

Sounds like mold temp was too cold. If you are using a bottom drop pot set the mold on the top to help it get up to temp. You have a temp problem.

Did you carefully sort thru your wheelweights and make absolutely sure there were no 'lead-free' weights in there. These use metals that will ruin a good pot of metal and make casting trouble-prone. There's a lot of tin and zinc , which will melt , but hardens fast , and makes poor bullets.

Ladle casting or bottom pour? It kind of sounds like a venting issue.

I've never seen a mold/alloy even close to proper temp fail to fill a cavity, even if it still has voids.

The 358429 was my first mold and I've cast 10Ks with no problem. I havent purchased a new Lyman mold in about 25 years, and I hear quality has fallen off. Having tons of ca 1980s WWs, I've never had to deal with zinc.

After the temp issue, I'd suggest adding some tin to that alloy, as well as some different pouring techniques. Whether bottom or ladle-poured, I never got good results pressing the sprue hole against the spout, I like about a 1/4-1/2" drop.

I havent tried them, but the guys at Castboolits swear by NOE molds. They're aluminum blocks, which I actually prefer as they're much easier to get up to temp. They surely have a version of the 358429.

Ok, last night I took the mould and did a couple of things. I took and scribed out the vent lines since they seem to be a little shallower than on my old 358156 mould. Then I took and cleaned the mould pretty well. Finally I loosened up the sprue plate a bit more. I didn't have alot of time this morning to do some casting since I have to work and had some other chores to do. In about thirty minutes time I cast more bullets than I got in two hours before, and they seemed to cast much easier with the mould and the metal the same temp as before (still using wheel weights and alot of the rejects from the last session). So I hope I have the problem licked, I appreciate all the help.

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Vaya con Dios

Are you fluxing the metal? Do you use a lead thermometer? I have an old Lyman furnace and a new RCBS furnace and their temperatures on the dials are way off. What is the diameter of the hole in the sprue plate compared to your other moulds?

Sounded like a venting issue to me and between the scribe and loosening the sprue plate you have managed a fix. On all my molds, I take one pass with a fine file at the parting line under the sprue plate. Just enough to allow the base to vent and fill. Sometimes a little TLC is all it takes.

The last time I used the mould after cleaning it I loosened up the sprue plate and it seemed to cast alot better. I flux the metal when I mould and have a RCBS thermometer that I get up to around 750-800 and the wheelweights flow pretty good in all my other moulds. The holes in the sprue plate are the same as in my older mould like my 358156 HP that can't ever seem to drop out a bad bullet, the same with my 358242. Both of those are older single cavities and casting with them is a pure joy.

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Vaya con Dios

If you smoke the cavities a bit, it will actually insulate the melt to a degree, and give you a better bullet. There is a NRA cast bullet booklet that has some articles WRT the sprue plate and hole sizes that may be useful (if I could just find mine!)

So it sounds like between scribing the lines and loosening the sprue plate, it was/is a venting problem. THere are acouple of fixes for that, one you've already done and another I mentioned in a previous post. If the mold still won't vent correctly, tell us and there are other fixes.

Lyman worked out the size of the holes in the sprue plate a long time ago. While they may not be perfect, they work. Some fellows enlarge them a bit but I have not yet found the need for that.

I know it sounds like a dumb question, but did you clean the mold cavity really good, like degreasing it, before casting?
There may have been a protective oil or coating inside. Also, I found that my molds had to be "broke in" with quit a few casts before they cast perfectly.
Just my thoughts Dave.