I ran accross a (6.5) 256 Gibbs Magnum sporter built on a 1903 Greek action and bbl at a show. Couldn't walk away from it for the price of $450.

There were also an entire line of (Rocky) Gibbs Magnum rounds made up in wildcat fashion (in the 60's IIRC) including a 6.5 version. Those are based on the standard 30-06 head size.

The 256 Gibbs Magnum (George Gibbs Rifle Co) is usually represented as being based on the 6.5 Swede cartridge with it's slightly larger head size.

With all that Al Gore internet info I went forth and expected my Geo. Gibbs sporter to be chambered for the larger Geo. Gibbs '6.5 Swede' head size version,,but it is not.
Standard 30-06 head size it is. I've since read where other owners have found the same thing to be true.

So my bargin priced used 6.5 Swede die set bought in anticipation of being able to be altered & used to make brass to feed the Gibbs sporter now simply pushes the shoulder back on 30-06 and 270 brass. With some trimming and carefull fiddling, I can make the Gibbs sporter shoot and is another fun range toy w/it's Aldis Bros scope in QD mts.

I don't know if the new brass being made is the old (Geo Gibbs Rifle Co) .256 Gibbs Magnum,,and if it is,,is it 30-06 head size or 6.5 Swede head size.

Or is it just 1960's Rocky Gibbs wildcat 6.5 Gibbs Magnum brass (probably not)

I made that more confusing than necessary didn't I,,sorry for that.