Well, I tested to see how much Trail Boss you can put in a .38 S&W case, utilizing Hodgon's technique of marking the case where the base of the bullet would be, this would be your max load.

With a 158 grain LRN, loading to the base of the bullet would give you 1.0 grains Trail Boss in the case. In .38 Special, 3.2 grains Trail Boss with a 158 grain LRN will give you 700 feet per second, so I'm guessing 1.0 grains Trail Boss with a 158 grain LRN in .38 S&W would be well under 500 FPS, probably too light for safety, too much of a chance of a squib load.....

So, I loaded 40 rounds with 2.2 grains Bullseye which should give 625 FPS, I'll try them tomorrrow and report back.