has anybody done this and where do get dies? any info would be greatly welcomed

Browning
I've not done it!
Curious though, the 25-06 was considered overbore for a lot of years, wouldn't this be off the charts?
Could you tell what hope to gain in the way of velocity, etc.
I had thought about using one of the new rimless magnums for sometinf similar. My thought was to make a 25 caliber equivelent of the 6 PPC. Short, fat, no body taper, sharp shoulder popping 100 grain Sierra Match Kings out a 3500 plus.
Jim

The slightly larger .25 STW has been done a few times. Of course, the old .257 Weatherby would be very similar, though of slightly less capacity. A .264 Win necked down .007" has been done, and gives virtually the velocity of the .25 STW.

Why do you ask?