I'm gonna stick my neck out here and say that the use of BB bullets is but one of the factors to worry about. Mike Venturino in Handloader seems to worry a lot more about cylinder throat and bore diameter than bullet heel design. Yes, a skirted base can cover a lot of other problems, but then bullet hardness and velocity come into play. At the operating pressure of .38 Spcl there are any number of powders that should work.