I don't see why you couldn't resize .25-06 to .30-06. I've resized plenty of .30-06 down to .25-06. I agree with Mr. Fischer that you should do it in steps. I also shoot .270 Win so I first neck size the .30-06 brass down to .277 and then run it through my .25-06 full length die. I get fewer "wrinkly" necks that way. The real question is, why did you sell your .25-06?