Here is an easy method to make your own Sprue. This little PoP form will make hundreds of sprues. By creating them hollow, this should help the removal of the hot wax during dewax. I'll try almost anything to prevent cracking the shell.
Thanks Mike. None of this stuff is expensive or too cosmic. Necessity is the mother of all invention. Same thing could be accomplished with a wood box instead of metal . You would just pull out the plaster form, soak in water, shake the water off it and stick her back in the box.