The easiset thing to do would be to slap a caliper on the neck OD before and after sizing. See if the diameter is changing... and if you are using enough pressure. These days ive been screwing my collet dies further into the press than the instructions say... and it works easier for me. If the mike shows that the brass is being sized, give lee a call and tell them your problem, they have undersized mandrels, though I suspect that you may not have to go that far.
Every once in a while the Colet die bashing bandwagon gets loaded and rolling... but id be happy to buy these defective dies if you folks are really that tired of them and its one I don't have. Theres still a few I don't have... Ive only got 9.
Don't need a 300WM though. Mine seems to be working fine. 2, 3shot groups at 400yds, with the right from a clean cold barrel, a half minute adjustment to the left, and 3 more from a fouled cold barrel. The bipod bounced kinda funny on the shot that dropped out the bottom.