Oh and these days for a bullet to be moving too slow to expand, it's got to be moving under seven hundred feet per second.
If you picked a good bullet anyway. Old school super-generic cup and core JHPs that haven't had any actual design work done to make the bullet work under a variety of conditions don't do well when there is heavy clothing present, or they aren't moving all that fast, or anything gets between the designated target on the way in.
It pays to pay attention to which bullets are being offered up for big contracts by people with the time and money to test what they're being sold before buying them, and copy them. Winchester Ranger-T, Federal HST, the Gold Dot is basically the gold standard for acceptable performance, these are the bullets you want.
They aren't priced outrageously, they don't rely on any weird bullet weights or hyper-high velocity (which usually makes a load a very erratic performer, and not a good choice for a short barreled gun), the way they work is easy to understand, they tend to do about the same job regardless of what reasonable object they get fired into, basically they aren't a breathlessly advertised bullet.
If the marketing material is hyperbolic, chances are the load is at best a mediocre performer, more likely an extremely unpredictable one.
