That body diameter really is correct. You can make usable Lee ammo by turning the rim of 220 Swift ammo to .443 and just necking it up to 6mm. It will be a bit short, but works fine. You will find the dimensions of the fired cases are almost indistinguishable form the unfired Swift brass except for the expanded neck. The head diameter is shared with the 6.5mm MS and the 6.5 Carcano, but there is nothing available long enough to make full length cases - the Swift is closest. I have tried swaging down 30/40 Kragicon cases, but that is real work. The solid head doesn't want to be swaged down a full 14 thousandths or so. You could turn the belt off 240 Weatherby cases, but they are hard to find and expensive.

Rifling twist is really fast so don't expect any accuracy from bullets lighter than 110 grains - if you can find the 105, 110 or 115 gr round nose bullets that Hornady and Barnes used to make, they work best. Otherwise, try the 105 gr. AMAX. By the way, you can make a size die by boring out the neck of a 220 Swift die with a carbide die drill, and avoid the cost of those custom dies.

OlManDow