I picked up a pair of the Oldfeller molds that the group on shooters ran, this is a 6.5 mm 160 gr bullet. I have yet to cast or shoot any from the wifes 6.5X55, but do know from the shooter clan that the bullet will be limited to 1600-1700 fps due to the fast twist of the swede tube.

Irregardless of that, I'd already conceived a wildcat to shoot that bullet. My first concept is to use a 221 fireball reamer to cut the body, then neck/throat seperately for a 1.5" long case, which will be formed from a 222 necked up, shoulder set back, and trimmed to 1.5". The advantage of such a round is, a) I have a 221 fireball reamer and b) if the case prooves too small to drive the bullet ~2000 fps, I can re-cut the chamber to a 6.5 BR, as I have a 22 BR reamer that'll nicely open up the body.

Herein lies the challenge/problem. The mold is designed to drop a .266" bullet in leu of military barrel/chamber specs. Modern 6.5 tubes are .264". My options as I see it are, cut the throat .264", and size the bullet .264", or, cut the throat .266", and size .266"

The former approach appeals to me as I really don't want to have to buy a custom throater for a single use. The question is, which approach would be predicted to provide the best accuracy?

Leave the throat at .264 and the bullet at .266. Every cast bullet I use shoots better at about .002 over bore size.

Throat it .264. You can go to .266 later if you need to.