Other than KAK I'm not really sure, these days you may have to get someone to open up a standard bolt face. I know JP, toolcraft, and maybe a few more make "high pressure" ar10 bolts with smaller firing pins and tighter firing pin channel clearance, but AFAIK they don't offer them in a short mag.
If I was going the route of opening one up, it would be JP...and I wouldn't load hot. I thought hard about building a 300wsm ar10, but figured there was a reason very few people still made them and stuck with good ole .308 and .243. That 24" .243 is a laser beam of death from a stand.
Now I'm wanting to see a SFAR sized 300wsm