You can purchase aluminium moulds but they have limitations, they are expensive and generally produce one or two at a time, they make 'professional looking' weights but it takes forever to make a batch of several dozen
Leads are not to be judged on their aesthetic properties but on their ability to give enough weight to cast a baited trace and to hold it on the bottom... so home made, rough and ready....and cheap.... leads will do the job.
Many years ago we decided to go fishing but had only a few weights and tackle shops were shut... so a quick think and the use of tools to hand resulted in the first 'cast in wood' weights.
Many people have told me that you cannot do this, 'the wood will catch fire', but you can.... and it doesn't. You will note in life that the 'you can't do that' types are the ones who haven't tried it.... and the 'yes you can' types are the ones who have.
A few minutes with a flat-bit in an electric drill drilling into pieces of timber, some copper wire stripped from an off-cut of electric cable and some lead melted in an aluminium milk saucepan with a blowlamp solved the problem. The holes were drilled with the wood on a concrete floor so the drill broke through the wood to give a small hole; twisted wires were put in the holes,the wood levelled up and the molten lead was poured into each hole. Some smoke ensued but no flames, so far, so good. When cool the wood was split open to reveal the leads, we made dozens of a three ounce version and they lasted us a good while, such is the nature of fishing that if you have plenty you seem to lose very few. Somewhere I have a photograph, will add it when I find it
Now that species hunting has taken over most of my fishing I am once again turning to this way of making leads. Leads are consumable items and, although small one (28g) and two ounce (56g) weights are relatively cheap the losses during a session fishing in weedy or rocky places can put a dent in your wallet.
So, back to the wood, drills and a bit of thinking. The destruction of the simple mould each time was no real problem...the wood used was off-cuts of no value and twenty or thirty leads were made from each piece. Experiments since have shown that when cool the wood can be whacked down hard and the leads will emerge from the hole.... obviously the smoother the hole the more easily the lead will come out....it turns out that the more leads you make the more the wood chars until a layer is built up, this makes the extraction of the leads far easier and a couple of whacks soon shifts them.
The next session was to make some ounce leads, a 9mm twist drill was used this time and the holes drilled into a pair of pieces of 2" x 1" timber so that instead of splitting the wood the mould could be parted along the centreline and the mould reused...this worked well and many 1 oz ( about 30g) leads were made.
Having the need of heavier weights, but having no bigger twist drill, the mould was modified by wiggling the drill from side to side to enlarge the hole, this resulted in some interestingly shaped 'coke bottle' leads. This enabled the production of loads of larger weights, 45 g , but at the cost of ruining the mould for making the smaller weights. It is a bit of a fiddle inserting the wires each time and reassembling the mould.... also the enlargement of the wire hole by constant use increased the risk of the molten lead escaping through the bottom of the mould; with the right sized hole the lead 'freezes' on contact with the copper wire and prevents any run out although there are gaps around the wire.
Two lengths of 2" x 1" planed timber were drilled with a 16mm flat-bit, the lead poured into the holes and the twisted wire dangled into the molten lead on an aluminium nail placed across the hole and resting on the wood.
This worked well and the resulting lead of about two ounces has a sharp edge that grips into the sand or silt, they grip surprisingly well if you tighten the line...and will roll in the current if you don't.
These weights are fine for smooth ground fishing but snag on rough ground, as they are cheap to make that is not such a problem when using a rotten bottom ( attaching the lead with a lighter breaking strain line than your main line so that the lead is lost when it breaks rather than the rig or the hook-length with the fish on it. )
So it was thinking cap on again to make a lead with a smoother 'nose end' that would pull through weed without too much snagging.
An impending species hunting visit to the species rich snag pit of Hobb's Point made it necessary to come up with a better way. To make a rounded nose the flat bit drill had to be made rounded, careful application of an angle grinder gave the required profile, the purchase of a pillar drill since making the other moulds gave the facility of drilling a smoother hole to an exact depth; the point of the drill could be brought to within a smidgeon of breaking though... a baiting needle the same diameter as the copper wire was pushed then through to make the final breakthrough.
Experience showed that the last holes were best not used as you need some spare at the end to whack onto a hard surface, as the copper wire is not doubled and twisted the leads come out fairly easily, and as said before, more use made for easier removal. The tails of copper wire are easily wrapped around a nail and trimmed with snips to make the loop ....although you will get sore fingers if you do 200 at a stretch....
The copper wire in this case is stripped from an old length of cooker wiring cable, scrounge some offcuts from an electrician or keep an eagle eye on builders skips.
The 12mm drill gave a weight of pretty near the ounce and the 16mm drill a weight of about an ounce and a half...
I did take a tenon saw and chisel to pieces of wood to investigate making a tapered square section lead, it worked but I am unsure as to the benefits of that shape over the easier to produce round leads.... we will see............
We will experiment further to see about making heavier weights at some time, obviously the bigger the lead the more heat has to be dissipated on cooling, this could mean the possibility of conflagration of the mould..... we will see...
Time for a disclaimer, we are sensible grown ups and suffered no death or even injury, we were careful to put plywood splash guards to protect against over enthusiastic filling, we had a bucket of water nearby to cool any burn sustained but kept all water away from the molten lead. We used an oven glove when holding the handle of the aluminium saucepan and added only dry lead to the melt..... and we worked outside in the fresh air to avoid being made crazy by the fumes from the lead.
I take no responsibility whatsoever for any harm that may befall you if you do something silly and hurt yourself or others after reading this. Safety glasses would be a good idea as well as having immediate access to a bag of frozen peas... a burn will be far less of a problem if the heat is removed quickly from the affected area, cold water immediately then a frozen pack against it to quicken the cooling, common sense works better as you don't get burnt in the first place.