Andrew Butchart writes:

I'd like to turn them into 10lb weights with an eyebolt on the top.

I've done this and it works great as follows. You can do 100 lbs of
casting in an hour or two.

[First, don't worry about (a little) grease and/or rubber, assuming you
can work outdoors away from the neighbors. You'll need a Coleman stove,
or gas grill with a side burner, or a turkey fryer. Same applies to the
steel clips or steel weights mixed in. It will all sort itself out as
slag floating in the melt.]

Make your melting pot from a cheap stainless steel bowl from Wal-Mart,
something larger than the volume of the largest object you want to cast.
Use pliers to form a small pouring spout on the lip. Use two locking
pliers (Vise Grips) to be handles on opposite sides of the lip.

Make molds from aluminum foil bedded in (unused) kitty litter in coffee
cans. Form the foil around a model of your desired shape--perhaps an
object already at hand, or an item you want to copy, something you carve
from foam or wood, or cylinders or blocks. The model shape obviously
has to slip easily out of the foil (has "draft"). I used 1/2 inch
dowels to cast lead rods, which I then cut into pellets for scuba soft
weight belts.

You can cast in steel eyes or other fittings in the bottom (forming the
foil tightly, securing with a metal twistie) or top (dangle from steel
wire from a coat hanger).

Take every precaution that a spill won't hit you or anything wet,
including your feet.

Vapor pressure of molten lead is very low, so while you should avoid the
vapors from the melt (do it outdoors), don't be paranoid.

Then lemme know how it turns out.