The #1 shell holder has been in my goodie box for years. It seems to be for .30-06-.45ACP group. It has a slot apparently for on-press priming.
The #27 is identical except it has no slot for on-press priming. No clue on what cartridge it fits (larger than #1).
Both should fit the same brand/design press. The securing slot is much larger that the current standard that was pioneered by RCBS years ago. Both have checkering on the upper edges, but #1 checkering is coarser.
Any info on the press these fit is appreciated. Also what catridge fits #27 ?
Henry