I picked up a Savage 110 that was re barreled to 35 Whelen. I did buy some factory brass , but had some 30-06 brass that my 110 in 30-06 did not like. some thing about the rim would make the bolt hang after firing, broke a bolt handle on the last case. All of the bad brass has a R-P stamp. So I started reading on necking up the brass to use in the 35 Whelen.
I have the Lee 35 Whelen dies and it does have a tapered neck expanded. However no mater what I tried, annealing, polishing and speed, it would crush the shoulder or split the neck.
So fire forming is the trick that worked. I did not do any annealing. Tested on 6 cases, all worked VERY WELL. I used Green Dot for the speed and being able to stand up to packing. 14 grans of powder, paper towel "wad" packed a bit. Now for the funny part, I used coffee as a filler, packed a bit and topped off with Crisco grease to hold the filler in. I fired with muzzle pointing up. This worked for me, not a split case mouth. The report was loud enough to need rear protection. The coffee was heavy enough the make the charge work as it should and the barrel was spotless to boot.