I just bought a .45 single cavity lead ball caster at a local antique shop in good condition for $10. I have been looking for one for a long time to cast lead balls for slingshot use. Any tips for this beginner? Thanks!

Try not to burn yourself...

Oh! - And don't sniff too many of the fumes that come off your lead (melting) pot.

what he said. wear leather work gloves when you are casting.

heat the caster your balls will come out smoother.
be careful and keep all liquids away from the molton lead. so keep your beer far away,but not to far.
Oh yeh saftey glasses to

So I should degrease the oil off before casting? Also what is the cheapest and best way to melt using plug in melters? Which ones?

Don't bother to degrease (unless it's caked in grease or cosmoline). At 850F, it'll degrease itself pretty quickly - again, just don't breath in those lovely fumes... I use a LEE 20lbs furnace (115V) that is a bottom pour. They also make a 10lbs "Production Pot" that runs something around $40 from Midway. Some people use a (non-pouring) dip pot with a laddle. I recommend the bottom pour for beginners. I would get some FLUX to help raise the crap and trash to the top of the pot for easier skimming. You can use candle wax (parafin) as a flux if need be, but it makes a lot of smoke.

While casting...

Don't:
Wear flip-flops.
Cast in the nude.
Flick lead at your kids, spouse, pets or "friends".
Sniff the fumes like your checking a pot of spagetti sauce.
Get any liquid (especially water) near the pot (explosively delicious!)
Cast over or around anything that can catch fire or your don't want scorched.

Do:
Cast out doors in a ventalated area with little (or no) breeze.
Regularly skimm off the trash on the top. (I use an old soup spoon)
Wear long sleeved shirts and pants and closed toed (leather) shoes.
Have fun.

If the balls start to come out wrinkled or mis-shappend (I hate it when that happens), your mold it too cold. Cast about a dozen or so and put 'em back in the pot. After, 12 - 15 pours, the mold should be hot enough to pretty up your balls (I love it when my balls get prettied up).
If they start getting a "frosty" sheen to them, your lead (or mold) it too hot.

MacBeau pretty much summed it up. I use a Lee Production Pot IV myself, and it works fine. For flux, about a pea sized piece of candlewax works fine, just stir it in immediately. It will smoke immensely, and may burst into flames, just keep stirring, it'll stop. Make sure to smoke the mold first. Degrease it THOROUGHLY and then hold it in the smoke of a lit candle until the cavity is well sooted up. This will keep the balls from sticking as you drop them. Drop them onto a folded up old towel, as at the perfect drop point, they are still a little soft. You can close the mold and set it on top of the lead in the pot to heat it, when lead no longer hardens to the outside of the mold, it's ready.

Most of casting is feel. Trial and error will find the right setting for the pot, the right pour speed, the right time to open the mold and drop, as well as everything else. The good thing is the bad product is reuseable, just put them back into the pot and remelt. You develop a rhythm, and it goes rather quickly. I work in the shed, no wind, but leave at least a window open, if not two, or a window and the door. A small fan set on low some distance away creates a light cross draft, keeping the fumes heading out.

I thought you were supposed to let the freshly cast balls fall into liquid to cool and harden?

^^If you want to harden (anneal) them for loading into cartridges, drop them into the 5 gal. bucket of water (with about 2" of sand in the very bottom). It hardens 'em up amd helps a bit with leading in the bore and make the bullets deform less rapidly on target...

For muzzleloading (minie balls, pistol/revolver balls, etc..), slingshot shot, you want them as soft as possible, especially if using an alloy with high tin, linotype or antimony... With fishing sinkers, it doesn't matter either way.

You can do that as well. It's not going to make a difference for a slingshot, though.

Mostly, shooters who want to use cast lead for high powered rifles, or really hot magnum revolver rounds, where the projectiles are being pushed really fast do that to keep down the leading. For low velocity, such as the slingshot or Blackpowder shooting, hardening is not necessary. For Blackpowder shooting, it's usually a detriment.