Originally Posted by mshaner
[...](i.e. 6.5-284 Norma caliber would be denoted as "5-26" where the 26 implies a .264 caliber)[...]
Correct me if I'm wrong. But, I don't beleive there is a .264 caliber. Rather, 26 cal is .264" in dia.
If you measure the insert, you'll find it to be slightly smaller than that since it represents a datum line corresponding to a typical minor diameter within a 26 cal bore associated with the lands rather than the grooves. ...the latter being .264".