Not as high as some are posting but 6 grains of HS6 with the Speer lead SWC with a magnum primer in 38 special is an absolute tack driver out of any of the 38 or 357 revolvers I have and was just under and over 900 fps depending on barrel length. The ones I loaded hotter to get close to 1000 fps did not have the accuracy and started leading barrel. The best accuracy and highest fps came from a 14-3 with a 8 inch barrel.
I couldn’t get 231 or Unique to give the performance that I got with HS6 though there are many other powders that others have.