useful tidbit from the old forum:
I've got a 358 throat impression sitting here. The freebore is 0.362" x 0.359" x 0.130" long (the gap between the case mouth and the freebore is included in the freebore length). I vaguely remember it being from a Savage but don't hold me to that. The leade angle appears to be gentle.
The Clymer website (another good resource for cartridge dimensions) lists a 0.361" freebore diameter and a 1.5° leade angle.