admittedly I've not read this whole thread, a bit long. However, returning from the range; I'm loading a Hornady 90gr.XPT ahead of 3.2grs. of Titegroup, and getting 931 vel.
at 9' from a Kel-tec and 960 from a Bursa Thunder.
Bullet expansion from the K-T in Ballistic Technology's "test tube" (a green waxy material) is .470". Penetration in this test medium from what I've been able to deduce is about the equiv. of 11-12" in ballistic gel.
I'm trusting this will work for social purposes but hope I never have to find out. If it doesn't expand, then it'll perform as a hard ball.
rev.