getfoxy,
I don't think leaving teh brass in teh oveen too long will cause what you have described. It easy or too hard to make judgements over the net, but it sounds like you are not fully sizing the brass and teh expander isn't adjusted properly too. Different cases feel different when sizing them.
I'd insert the die in the press, adjust it so when you have the lever pulled down it is touching the ram and then turn it another one screw turn down, lock it in place, then screw teh expander pin down until the end of the pin is protruding about 3/8" below the bottom of the sizing die and then size a lubed case all the way down to touching the ram again.
Let me know how you go with that.
