Learned a couple of things. Throating for the 100 grain bullet makes sense as the 264 was touted as a dual purpose varmint/big game cartridge. I don't believe Bob Hagel mentioned this in his load work up and review of the 264.

Those Noslers are unique, I thought the Zippeedo was their first boat tail but those partitions look like they pre-date them.

The .263 diameter bullets were for the .256 Newton and some European 6.5mm's with a .256 x .263" groove & bore diameters.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli