Years ago I bought one of these collets (less the new shim) and it fits my RCBS fine. The nice thing about it is that the O-ring is crimped on the three aluminum pieces so they never separate. It's also split so you don't always push the bullet through a circle. I was always having problems with the collet assy. becoming 4 separate pieces.
I've had mine for 8 years now and it's still going strong.


Uni-Chuck "Shim-Fit" Combo — Quinetics Corporation