I know the folks that produce thiscasting plastic was a lot harder than I thought it would be. I tried making some molds and cast some marble size pieces, man it went bad. might have been the 2 part resin I bought, but everything that could go wrong did. air bubbles ,over mixing, and poor mixing. I had a sticky gummy mess, then the next try my resin hardened in the mix cup before I could pour it.
I say all that just to say it might not be as easy as it sounds. when we investment cast at work, we have a pressurized and heated wax pot (toy custom parts makers use the same but with plastic) . we also have a vacuum chamber/casting table to help get the bubbles out of our vestment and draw the liquid metal into the mold when we pour.