According to my Hornady manual, Vol 1 fifth edition, the .380, 9mm luger, and .357 Sig all use the same bulets. My Lyman also showed these three sharing a few of the same bullets, but according to Lyman none of their molds will make a cast bullet suitable for the Sig. However, Meister has a cast bulet listed for the Sig, so maybe you can try 100 of those for range use.
It seems to me like any .380 bullet would work, unless it has something to do with the lube groove interfering with crimp and correct OAL. I have some 100 gr truncated cone bullets for my .380 that look like they might work, but this is pure speculation on my part.
There just doesn't seem to be a whole bunch of data or components available for the SIG.
GH1