Getting a good source of lead for casting your own projectiles can be difficult. Yes, you can try to get lead wheel weights from the tyre shop (but these are rapidly being replaced by other materials), from ballast used in boats from a boatyard, from scrap dealers or from metal merchants, from used diving weights and sinkers; but you do not have to expend that much energy if you use range scrap to your advantage.
Range scrap is just the fired lead that ends up in the sand stop behind the range targets. With just a mesh screen, a spade and some time (or the kids) you can rapidly collect a few pounds of lead. The other advantage of range scrap is that it already have the correct additives to the lead to make it a bit harder as pure lead makes you barrel very dirty.
When you are melting down range scrap, you will need not only to melt it down but also clean up all the sand, copper etc that comes along with the range scrap. This is done simply by melting the lead and then using a fork or a sieve to remove the dross from the top of the molten lead (lead is a very very dense metal so everything floats to the surface, including copper). Once 95% of the dross is removed, adding a small amount of candle wax or bees wax into the pot and giving it a stir will not only stink and smoke a lot, but also make any impurities left in the lead float to the surface for removal.
Once you lead is clean, use your dipper to pour it into lead ingot moulds and your done!