I doubt you will find published data for Red Dot in a 20. I am assuming you desire to load 7/8 oz.
Years ago I did extensive pattern testing of 8's through chokes ranging from cylinder through .012 or Lt. Mod. I tested 800x, Unique, Universal, 20/28(which was new at the time), Green Dot, and Winchester WSF. I also tested International but discarded it because of the pressures it generates. Shortly thereafter Alliant pulled all of their 7/8 oz Green Dot loads from their published data citing erratic pressures in some load combinations. Regardless the load, I never achieved anywhere near suitable results through cylinder choked guns (4 tested). I did achieve the most consistent results through chokes .006-.012 but never tested any chokes tighter than that. The criteria I used to make my decision was clean/complete burn, pattern consistency and repeatability, velocity consistency, load metering through a Mec 9000, hull life, and availability. My results were 1)WSF, 2)20/28, 3)Universal, 4)Unique, and 5) 800x.
Since then I have loaded close to 70,000 WSF shells and have had not one problem through all temperatures. Even during the powder shortage I was able to locate WSF with a bit of searching.
My current load:
Remington STS hull
Win 209 primer
Claybuster 1078-20 wad
7/8 oz of Eagle magnum 8's
16.7 gr. WSF
Velocity at approx. 1175 and pressure in the low 10k range.
Hope this helps.
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