The Hornady SST is Hornadies answer to the nosler Ballistic tip. Both are cup&core hollow point bullets with a polycarbonate tip in them. The tip helps initiate expansion, they work quite well, all TOO well. The SST is an interlock bullet, the ring at the base is SUPPOSED to hold onto the lead core to limit the tendency of the core to come loose from the jacket. It doesn't work!
I used this bullet in several rifles. a 300 WSM, a 7mm-08 and a couple of .280's. In every case when Wisconsin whitetails were shot, the core went on through, the jacket was just under the skin on the opposite side. Bloodshot meat around the wound, and lead shrapnel all along the bullets path.
I'll qualify that by saying, the deer were DRT, dead right there. Effective, yes, optimal, no.
As for what happened to that target, you dropped one low and left. One target is not a good test for any load. Ten targets might be. By asking that question, you're saying everything else was perfect when you let-off the shot. Somehow the bullet wasn't accurate? I've been shooting for 55 years, even I pull a shot once in a range session. Shoot some more before jumping to conclusions.