30-'06 cases are easily turned into 35 Whelen cases. I've been doing it for about 15 years with no problems. If you have a good supply of '06 brass, it makes perfect sense to make up some Whelens. I have used RCBS 35 Whelen dies and Imperial Sizing Die Wax with new and fired brass with excellent results. I lube the inside of the case necks. After sizing, I run the cases through the tumbler. I have never had to fireform cases for my Remington 700, just run them through the die, load and shoot. Be sure to keep a check on case length.
