I'm new to this forum. I was directed here from another forum, where I posted these same questions but with no responses, by Jon A. Looking for loading data for this wildcat. The project was finished 10-12 years back before the introduction of the WSM and RUM cartridges. I just recently got the rifle from the gunsmith (I moved before it was finished). I will be using 300 gr. Sierra MK bullets. I figured I might as well test it out before I have it rechambered for some other hotrod 338 cal cartridge. I have the following slow powders in my inventory that I think might work for this combination - H-1000 Retumbo RL-25 N-170 AA-8700 H-50BMG IMR-5010 WC-860 H-US869 WC-872 Any guideance would greatly be apprecaited along with any suggestions on a firefoming load. Thanks.