With my first muzzleloader I exclusively shot the 240gr Hornaday HTP. I killed more than 30 deer with that bullet at ranges from 5 to 198 yards. The only one that I ever recovered penetrated from the tailbone up through 4 vertebrae, angled down and forward and lodged on the back edge of the sternum after taking out a lung. It had expanded somewhat, but not hugely given 3 FEET of penetration (deer dropped in its tracks).
All of the other deer were chest shots and dropped within 30-40 yards. I never cared for more expansion as I figured it would jsut ruin more meat on the exit side. The deer didn't seem to know the difference!
The SST does appear to be a poly-tipped XTP. I've heard varying reports of their expansion, from good to not at all. Of course the deer still went down in these reports so it seems ok to me.
If you really want expansion and shoot 100 yards and under, go with the Keith Nose HP from Precision Rifle. I think they turn into half dollars!
I'll be sure to report back when I've bagged a couple deer with them.