I used to use International Clays for 20 gauge, but they don't make that any more I guess. I have about 40+ boxes of shells loaded and a bit left in my jar. So, I bought Hodgdon Longshot. I haven't used it yet. There seems to be plenty available and there are formulas for 1 oz. 20 gauge on the bottle with instructions to check their listings of all of there data on their website. So, I'll see. I still use my 1 1/8 oz. trap load for everything I shoot with a 12 gauge. Good luck.