O.K. deadwood, you're right.... My 6-pack of Hornady inserts didn't include the 6.5mm insert either. I called Sinclair and they were kind enough to send me a single 6.5 insert......... Ask them very humbly and they might do the same for you. Better than buying a 14-pack for one lousy insert..................... Mean while use your .257 insert to measure CBTO. The measurement will come from a different point on the ogive but will otherwise be consistent. If you use the .223 or .243 the measurement will come from a point on the ogive which is much smaller in diameter and where inconsistency in measurement is more likely to occur. Itty bitty groups to ya', Dale