I have a Remington 700 in 35 Whelen, with improved chamber. I really like the rifle. I understand that it is possible to fireform brass from 30-06 cases. Is anyone familiar with this process ? thanks for your help.

If you have the right expander ball in your 35 die set you may be able to just run in the cases. Should have a taper that will start in the 30 caliber neck. Otherwise do it in a couple of steps.

Witness,
T_Bob is correct about expanding the necks. Now, for fireforming the cases you should be able to use a charge of 12-14 gr. of Unique and a 158 gr pistol bullet to blow out the shoulders. The headspace is supposed to be the same between the 30-06 and the .35 Whelen and Whelen Improved. However, if when trying the fireform loads you notice headspace problems, then you'll need to seat a long bullet (like the 250 gr Speer) out far enough to engage the lands and thereby keep the round from being pushed forward when the firing pin hits the primer. Use a starting load for regular .35 Whelen when you do this because the pressure will be increased due to no bullet jump before hitting the lands. Do you know any local wildcatters who might help you learn this process? If not, you should read up on the subject first.
Jerry/AK

In the 35 whelen I had, I lost alot of cases because the shoulder was too far forward. When the cases fireformed, the firing pin drove the case forward, and created excess headspace on the brass. With future firings, the case heads seperated.

If you have the Redding 35 whelen AI dies, they have a tapered expander, and will neck up -06 brass nicely. The only thing is, after necking up and blowing the cases out, they come out a bit short 2.45" vs 2.49". If you want proper length brass, you can neck up 270's.

I found a 180 gr cast pistol bullet and 15 gr unique to work well. Lighter loads didn't fully form the shoulder. Load the bullets long so that they engage the lands to prevent the case from moving forward.