3.0 grains of Bullseye will get you a nice light recoiling load in the mid 600 fps range. The cases may come out sooty because the pressure is very low.

I like Red Dot for light loads because it generates peak pressure quickly and seals off the case and burns completely. 2.8g of Red Dot under a 158g SWC feels a little stronger than a .22 LR and is great for easing someone into a centerfire pistol. Other fast powders good for light loads are Clays, TightGroup and of course Trail Boss which was meant for light loads in black powder cartridges.

With light loads in 38, be careful of double/triple charges, its a big case. That's the other good thing about Trail Boss, it takes up most of the case volume with a single light charge.