crushing case necks when using expander mandrel to open case neck on a 338SS

[Calvin45]

I had this exact same problem with the 338 sherman max. I used the 21st century 7mm to 308 neck up expander, but at the time they did not have the 308->338, and by the looks of it they still don't. I tried using a straight 337 mandrel, crushed cases. I had a buddy with a lathe make me a 308->338 with the same taper as the 21st century ones. Still got a lot of collapsed cases. Of all the things that finally worked was just running the 308 necks through the Hornady FL die with the expander ball in there with all of the cases chamfered and graphite as lube. I'm not sure why an expander ball works better than a much more gradual neck up expander mandrel.

That is surprising!

There's always the intermediate 8mm step as well…

 

[Mike Matteson]

.338 is on the left .308 is on the right

I am late to the game, but. Looking at the pictures I see this might be the problem. The O.D. of the 308 is about the same size or just a little smaller than the bevel of the 338 mandrel or so close that I feel that could be the problem., Looking at that OD sizes the 308 is .3080, 8mm .3230, and 338 is .3380 bullets. So there is another step that could be put into place.
I down size .284 to .243 necks. It takes me 4 steps to achieve the down sizing of the neck on my 280AI case to .241 I.D. I am setting up to anneal in the middle step as avised to.