I started with Federal GM 06 brass no problems but switched to Lapua its great no problem and goes through a die like butter. I have never had your problem.Wish you luck

Rob1SG stole my reply. I have used the Federal Gold Medal Match with ZERO problems. I have reloaded some of my FED brass 6 times already. Never ran into the problem you described.
I'd check my DIES against the case dimensions for the .338-06 in one of the loading books. Make sure that your neck is being sized enough and/or the ball on the decapping pin isn't too large.

FN in MT

Frank, as usual has a good point. Try sizing w/o the exp. ball in place & see if things straighten up. Then you'll have eliminated one variable.

Sounds like you have a die problem or a one-time brass problem. I have used both '06 and 35 Whelan brass with good results except for one batch of nickel plated brass which neck split after about the 3rd loading. I now use 35 Whelan exclusively just to have a headstamp unique (even if inaccurate) to that rifle.

OK I have done a little work at the bench and here are the results so far: LoL



I have three current reloading manuals that show case dimensions for the .338-06 and all three show different outside case neck diameters! Hornady defines the neck as .370"; Speer specs .365"; Nosler comes in at .369".



Now I did what a few people have suggested and ran some newly reformed .30-06 cases, (3 of each: Federal, Winchester, Remington brass and Remington nickle) through my RCBS FL sizer die a second time but with the expander ball removed. All the cases, from 3 different manufacturers were all reformed at .360" outside neck diameter, which is tighter than the "loosest" dimension from any of my manuals and as such should give the expander some case to push back out . With the expander ball in place all the cases measured .362" outside neck diameter. On a whim I ran a Winchester .270 case through the die and it came out with a .360 outside neck diameter. The expander ball btw measures at .334"



I think that as the tolerences are so close here, a matter of only a couple thousands of an inch, that even the slightest thining of the case necks is being noticed. I am going to have to pick up a ball micrometer and check to see just how much thinning is going on.