So... say I want to make an AR mag well insert for a caliber and magazine conversion. What material lends itself best to a casting that can then be altered to accept springs, latches and pivot pins? A plastic? Epoxy? Some sort of resin? I basically need to make a bunch of "blocks" about the size of a 20rd AR-15 magazine that has room to hold a 1911 magazine inside of it, and tweak each one to find the best depth for the magazine to insert, for reliable feeding. I will then take that plastic model and look into a CNC metal (probably aluminum) solution that is more stable and rugged.