Since the BBwc can be pushed harder, since it does not have a "Skirt"...........

I found one old note that stated 2.8grs of Red Dot at 660fps.
This is probably out of a M19-5 6", since I do not recall shooting
a BBwc through a J frame snub nose.

My guestament figures right now are.........
3.6 up to a maximum of 4.2grs of BE-86 powder but they will NOT
be tested in a J frame........ a K or heavier frame is the way I go with unknown data, in 38 spl. loads.
Once I have a number to work with, against other data I will raise or lower the charges.

Stay safe.