This Instructable will teach you how to cast an aluminum slingshot capable of great power and suprising accuracy. The actual casting method used is "lost foam casting", in which foam is carved into the final design and buried in sand. Metal is poured into the foam, vaporising it and filling the mold cavity to make the final object. The basic slingshot design is Joerg Sprave's Rambone slingshot, although I did not use any templates in the creation of this slingshot.
I decided to do this one day when I had seen a video on making a lost foam aluminum slingshot. I had tried greensand casting (https://www.instructables.com/id/Cast-an-Aluminum-B...) and lost wax casting (https://www.instructables.com/id/Cast-a-Metal-Ring/), so I decided that I should try this last common method of casting in order to more fully master the subject. I also got hooked on slingshots after seeing Joerg Sprave's videos on YouTube.
Enough talking, let's get slingshotting (yes, that is an actual word)!
First off, get some foam. I believe polystyrene foam (aka Styrofoam) works best for this, so try to get some. It should be very common - I heard that furniture stores might even give you some for free. I started with some oddly-shaped box inserts made of Styrofoam and began to butcher them with a large kitchen knife (pic 2). Once these were cut into nicer flat sheets (pic 3), I glued them (woodglue) together to make a thicker block (with an extra-thick part for the handle) and compressed (using iron railroad spikes) them to get rid of any space in between the seams (pics 4 and 5). Basically, you need a block of Styrofoam; you may already have yours in the right shape.