My 686 6" with a 158gr XTP real copper coated bullet and Bullseye powder with that load reached 770fps in one of my test loads.
Red Dot did 832 and a +P load of Unique did 976fps.......
all c/o a 38 special case.

With light loads, ALWAYS look for a new hole in the target or flying dust, to be on the safe side.

You did not state if that was a lead or plated bullet, since that company makes both types.

Good shooting.