Stocks that fit like the 90-T, 870, 1100, Ljutic etc are the simplest to cast.
For tanged guns with stock bolts, altering the inletting just a very little bit can cast a stock. Glass bedding will be needed.
Acutal bending needs to be done on those guns without a stock bolt, ie S/S's.
If heat is used, extra care needs to be taken because some finishes will blister.
Doug