I don't load 20 ga these days, but there's a company called Ballistic Products Intl which deals in all sorts of shotshells and reloading components. They even have their own data gathered for nearly every guage. They market (or at least used t0) Cheddite hulls, both primed and unprimed. You may be able to go on line--they have a website--and find some neat info. I bought a goodly supply of their 16 ga hulls and wads--the Cheddite hulls are excellent, and for a guage like 16 their wads are the best you can find IMO.
