Has anyone seen this stuff yet? I'm wondering were the extra 4mm came from, is it in the case body or the neck? If its in the case body and corresponds to a higher capacity, anyone gonna play with the brass with some different bullets?

IIRC, the added length is in the case body. The neck on this case is surprisingly short. During initial development, the head of ammunition at Sako used a standard 9.3x62 reamer and ran it in an additional 4mm. The increased capacity seems negligible when compared to the x62. It is a cool cartridge but I'm not sure if it has much of a future, at least here in the States.

The 66 case is simply the 9.3X62 with an extra 4mm in the case body. Shoulder and neck are exactly the same as the 62. While you pick up several grs of gross capacity in an 06 lenght magazine the net gain is very small. The bullet seats deep and the only gain is the small area between case wall and bullet. In a longere box you can take advantage of the gross capacity.

I drew this up when I was thinking about a 9.3 wildcat.

If you can't find the 66 brass it is easy to make using cylinder brass.

Well Federal does load the 9,3x66 in the US as the .370 Sako Magnum with either a Nosler Partition or Barnes TSX 286gr bullet in its Premium line so at least here we don't have to await Sako loaded ammunition