I have a lyman 450. I got it with a .452 sizing die, and with a top punch in it for swc. I unscrewed the sizing die and he die and threaded collar come out as one piece. Are they one piece or just stuck together? If they are one piece, why doesn't the rcbs .357 sizing die I just bought have a threaded collar on it as well. It just has an o-ring on the top. Does the rcbs sizing die even work with the Lyman 450?

Two seperate peices.

The O-ring seal sometimes causes the nut to stick to the die. Do a little wiggling and pulling and they'll come apart.