The early ones have a square flange under the barrel, but this was later found unnecessary. I'm told it can be removed by sweating it off but I do not know this for sure. Also, it might be possible to modify the bedding of the later rifles to fit the early barrels. However the bedding is steel and looks like an engine big-end bearing, so I wouldn't assume the stock could easily be modified either, to make a recess for this flange just in front of this bedding shell.

Beware too, that some have a barrel ring for the front swivel. Others have a swivel in the fore-end. So if you get the wrong barrel, you might have 2 different systems on one rifle or not be able to carry it afield without doing some modification.

7x66 SEvH is a great calibre, but getting the cases can be problematic. Mine puts it's shots in a cloverleaf at 100 yards. I don't ask for more than that. If anyone is considering modifying .404 cases to make 7x66 SEvH, I suggest you price the conversion dies first. They might cost as much as the rifle, (albeit, not as much as the Koelner Jagdhuette rifle shown). And you'll still have to use a mini-lathe to reform the extractor groove.

The 8x68S Mauser 66 was actually very popular for overseas hunts. A flat shooting powerful cartridge combined with a telescoping action and a barrel-band front swivel meant a compact rifle to carry, much shorter and about a pound lighter than say a .375 H&H. In theory the 8x68S barrel can be fitted to a standard stock, but the bullets need to be seated deeper to work them through a standard action. This is according to Australian arms authority Nick Harvey who reviewed one. I have not tried it with mine. The 8x68S was reworked with shorter bullets by RWS to work through a standard (i.e. .30-06 sized), action and the RWS KS bullet was pretty revolutionary at the time, which added to this combinations popularity in the Mauser 66. The Mauser 66 was the first of the new-generation "switch-barrel" guns, now seen in a variety of other makes such as Blaser R93.