Your 30-06 and the first persons 243 should be a small shank. To be certain just measure the length of the barrel nut. If the barrel nut is 5/8" long it is a Large Shank. If the barrel nut is 7/8" long it is a small shank. Be sure you are measuring the barrel nut only. Several customers have measured from the front of the receiver and then they are including the recoil lug thickness as well.

Jim Briggs
NSS