I load for the .17-223 and with H-335 and a 25 grn. Berger bullet with Rem. 7 1/2 primers my max. charge seems to be about 20.4 grn. of powder. The .223 case is about 7% larger so if you start with a load of about 17 grns. of H-335 and work up 1 or 2 - 1/10 at a time till you start seeing presure signs you shouls be all right. If you haven`t played with wildcats be very carefull and if in doubt don`t do it. The rifle you have should be a great shooter and a great varmint rifle, a tou I would love to play with, but custom rifle in wildcat chambers can be dangerous. BE CAREFULL.