I’m in the same boat (but hey, at least I have brass and primers). It’s a new cartridge for me, but I have scrounged up some Accurate Magpro, Ramshot LRT, and US869. I found reports of each being used successfully in PRC and similar capacity cartridges, so I’m hoping one will work. I also found published data for the 4350 powders and I have SW4350, which is supposed to be the slowest of the group, so I’m going to try that as well. Just waiting on the bushings to get here and then I’ll start testing.