I have solved a couple of problems like this mostly by luck. Doing a little math with cartridge drawings from various sources, and a dial caliper, I discovered that Wilson case trimmer shell holders solved a couple of my problems. I seated my checks on the downstroke of the drill press quill, through or just partially through the Wilson holder. They are hardened and polished, self centering and do a bully job. I am not familiar with the dimensions needed for seating .348 ish checks, but I'd think you might get lucky with something like the .32-20 for example.
