WST is a great powder. Used it in the past and recently came across some more. 19gr. in a AA or STS/Gun Club hull with a 1 1/8 wad is a VERY good 1145fps load that shoots very soft.
20gr. will get 1200fps but you have to watch the components so that pressures do not get to high. 20gr. is a good 1oz. load that I have had not as much success with as the 1 1/8oz. load.
See the loading data on Hodgdon's website.
WST has been a good powder for me. I'm using a lyman 5th edition load; 19.0 grains in a AA hull (old style tapered hull not the HS) with a 1oz AA12sl wad, 1oz of #8 lead, with Win 209 primer. A very soft load that shoots consistently (well when I do my part I guess, 94/100 last time out and some very nice ink balls thrown in with some lucky breaks w hard rights on 5)
Patterned this recipe and it was decent as compared to anything else I've tested. It did seem do put a more concentrated amt in the center but was at 26 yds when testing. Lyman and others list some other loads with 1 1/8 oz and with Fig. 8 wads, as well as DownRange Jammers that I've been tempted to try but I'm happy with my 1oz so far. I've been trying to save a little so I'm sticking with the 1oz load.
I've used Fig. 8 and they seem even softer and load very well. Also windjammer wads blue? 1oz. worked/crimped well so you may want to try them or Fig 8. From what I've read, the most consistent was with win wads, win primers, and of course the win compression hulls. Go figure. It's like Winchester did some kinda homework and testing.
Make sure to weigh your throws and use a true recipe from either Winchester/Hodgdon or from your favorite loading manual. I was off 2 bushing numbers for my lot of powder from what the chart suggested to use, but it has been consistent once it was all set up. 19.0 -19.1 on elec. scale w I check.
It does tend to burn a little dirty for me. It seems the lighter loads don't burn as clean as Clays or some others that I've tried. I am shooting in some hot weather too and it seems to burn a little cleaner when it's hot out. I think today we hit 110 degrees or maybe 111. I don't mind but try and finish up by 9:30 a.m. I recently purchased a few more cans and think I will continue with it until I run out.