I have a few tips. Every time I make a custom mold for somebody I test it. Often they have given me directions which may make it difficult to pour. Of course I told them that when they said it, but when they argue I figure its part of my job to "make it" pour anyway.
- Place hooks and hardware in the mold and set the mold on top of the lead pot to warm up. A preheated mold will allow the lead to flow for a fraction of a second longer.
- Use a bottom pour pot and press the nozzle of the pot against the sprue opening before opening the flow gate. The weight of the lead in the pot creates HEAD PRESSURE helping to force the lead into details from the weight of all the lead above.
- Keep the bottom pour pot FULL. This creates more head pressure.
- Lightly dust the mold with talcum powder. The small particles of talc break up the surface tension of the lead allowing it to flow better.
- Lots of folks will swear by a stingy coating of candle smoke or a coating of graphite spray. Those primarily work as a mold release. Unless your mold is coated with a solder flux and is hot enough to melt the lead directly the lead generally doesn't need a mold release. (Don't do that) They have less affect as an agent to help with filling. A heavy coat of graphite does act as an insulator. It can add a fraction of a second to the freeze time to allow the lead to flow out better.
- I have had to come up with a recipe once or twice that included both a graphite spray and then a light dusting of talc, but that is exceedingly rare. If its one or the other talc almost always works better.
- Yes, sometimes the space allowed for flow can just be to small. Most of the time some combination of the tips above will over come that. Sometimes the answer is you just have to drill out the gate, but its likely the gate was made that size because of some customer demand of the past. Larger gate flows better, but requires more cleanup. If you do drill out the gates set the depth stop on your drill press so you don't destroy a cavity, and only upsize a little bit to start with.
- Some alloys will stick to an aluminum mold. Tin and some pewters come to mind. For these a mold release may be a very good idea.
- Lead does not "stick" to aluminum, but a shape with perpendicular surfaces and no draft angle may need a little help.
- Bismuth flows more than lead, so you will have to count on more cleanup if using Bismuth.
Please add your own tips for casting lead and other metals for tackle making below.
Also Worth a Read
Dripping Lead Pot & Reactivity of Steel At Elevated Temperatures
https://www.tacklemaker.info/index.php?topic=41.0
It pays to periodically check whether or not your pot itself of flowing properly. It may need to be cleaned out, and of course make sure your lead melter is reaching the temperature you think it is.
Contaminated lead. No matter how careful you are will eventually have lead flow issues with a lead pour put. Clean it out, however one item I have not addressed is contaminated lead.
I've been fairly lucky, and I tend to only use know near pure lead or specific lead alloy from a trusted source like Roto Metals (https://www.rotometals.com/). I might also use a source like Plum Bum (https://www.pbcastco.com/). Plum Bum (https://www.pbcastco.com/) does not guarantee a particular alloy exactly, but they precast the material they sell and sort it by hardness.
I do not endorse either Plum Bum (https://www.pbcastco.com/) or Roto Metals (https://www.rotometals.com/), but my luck with them has been good. Your mileage may vary.
Now, if you are just searching for the cheapest source of lead you will undoubtedly get a bad batch. I can't give you as much advise here. As I said above I buy lead from "trusted" sources. Commercial lead suppliers. If you are breaking down old sail boat keels, scavenging old wheel weights, and grabbing dive eights when you get the chance there is a high likelihood you will get some garbage lead. Zinc is the big one everybody parrots off, but I have seen "lead" wheel weights that show red rust. You only get red rust as far as I know from iron or iron alloys (steel).
Zinc is also a casting metal. Many parts in your home are certainly cast from Zinc (probably Zamak 3). However its my understanding it just doesn't play well with lead.
In any case its possible that if you get to a point where you just can't get it to go no matter what you try you may have a contaminated batch of lead.
There is where I sometimes have issues. I always test new design molds in the shop before shipping. I know if it works and how to make it work, but I always use know alloy from a trusted source. It may require just the right process as noted in the first post in this thread, but it will work. When a client then has issue with their castings I don't always think to suggest they try a clean lead melter with some known good alloy.