The dillion dies seem to be longer. The tool head for the 500 is a little thicker than a regular press and you could run out of thread on the sizing die if you crank it all the way down. Dillion dies don't run out of thread. Hard to explain. try a lee sizing die and you'll see what I mean, their thread area seems to be short. hmmm..
I got a feeling I just may have confused the whole issue there..
Yours in thread space