Back in the 70's I used 2.8 grains 700X with a 148gr. HBWC in 38sp. It produced 777 Fps. Nice shooting round. Your results may very. Start low and work up. Be careful. Second addition Lee book shows 686 for 2.0 grains and 804 for 2.5 grains of 700X. You might start in that range.
Good luck and go by the book.