+1 for what Phil said...You could just buy one of those micrometer seating tops, in .20 cal, and put it in the top of your seating die and go for it.......http://bulletin.accurateshooter.com...w-micrometer-seating-stems-for-standard-dies/
Phil.
The Forster .223 micrometer seating die with their .204 stem works fine too.I use a Redding 223 Remington Competition Seating Die and a Redding Competition Seater Die VLD Stem 20 Caliber - Long. I tried the Forster .223 micrometer seating die but the tips of 32 & 39 SBKs hit the seating stem causing varying seating depth. The Redding combo works with all .20 bullets and will give consistent depths. Gunstop was the vendor.