I always melted lead into a mold that I used during my asphalt days. It was an old chevy valve cover. It makes alot of sense to change the shape of your mold rather than changing the shape of lead. Lead is very hard to cut-- it jams the teeth of any serated blade and when the blade gets hot, the lead melts locking the blade in the chunk of lead. Drilling is easier if you drill very slowly. If you drill quickly, the lead will get hot from the drill bit and will try to mold around the bit and then it's a nightmare trying to get your bit back. I've found it's almost easier remolding lead than trying to cut it. So:
1. Make yourself a nice mold in exacly the shape you want it.
2. Use a propane weed burner (looks like a long torch with a vegetable can mounted to the end. Runs on a BBQ propane tank.) to melt the lead in a coffee can with a long handle attached to it. Do your work in the middle of a gravel driveway. The melting lead can give off some nasty fumes.
3. Pour slowly, If it splashes, it sticks to and burns whatever it touches. A long handle mounted on the coffee can keeps you out of the way. You can also heat your mold with pieces of lead in it and add more from the can to fill the mold.
4. After the mold is full, let it set for at least 2 hours. Lead takes a long time to cool.
5. Drill slowly. If you drill quickly, you won't save a bit of time if the bit bogs down and the lead melts to it.
MOST IMPORTANTLY---Do not let moisture or water get into molten lead!! Dripping sweat, spilled soda, a garden hose--and a very violent and explosive reaction occurs!! The lead will literally jump out of your melting pot. Never, Never, Never let water near molten lead. You will get hurt. You will lose flesh. Just let the lead cool on it's own in a dry place. The time you save trying to cool it faster isn't worth an eye or a trip to the hospital with hot lead stuck to you. Wear an old leather coat if you have one, wear safety glasses, wear a hat, wear welders gloves. I've melted probably 450 lbs. of lead in my life, and this is just what I've learned over 12 years.
It's easy to do, but you have to be methodical about your safety.
Scott