The other thing to watch out for, particularly with the Forster and similar 'clamping' style die rings (Whidden, Lyman, etc.) is that you don't have anything protruding from the ring, or if so, that that protrusion is facing forward, towards you. If something sticks out to the side or rear of the U-shaped slot for the die, then the die may not line up with the shell holder quite right, and it can cause all manner of problems.
That can also happen with some other kinds of dies - usually I've had issues with expander mandrel dies that were intended to sit low in a Rockchucker, not in a Co-Ax - so the die has to be screwed 'out' further than normal so that the top clears the U-slot. In theory, something similar could happen with the wider portion of a micrometer/sleeve seating die...