Its not what you lose if a HP fails to expand, that's not the problem
It's what you give up IF IT DOES expand that's the issue
Right. There is a lot of 380 ACP ammo that stops short of 10" of penetration but the Federal Hydra-Shok and the Hornady XTP (especially Precision One's loading of the XTP) are examples of 380 hollow points that penetrate to around 12 inches or past 12 inches when they expand. When the Hydra-Shok fails to completely expand (through denim), depending on if there is partial expansion or no expansion, the bullet is penetrating between 13 inches and 19 inches. I don't know if those 5 shots can be extended to represent your statistical chances of any particular bullet performance, but for the sake of argument if you were using the 380 Hydra-Shok you'd have an 80% chance of the bullet penetrating between 13.5 to 15.25 inches and only a 20% chance of the bullet penetrating to around 19 inches. If you're using an FMJ you have somewhere around a 99% chance that the bullet is going to penetrate > 19 inches every time. The Lehigh Extreme Penetrator may be an exception to this - but regular ball 380 ammo generally zips right through 18" denim covered gel blocks
https://www.youtube.com/watch?v=v7uG-13LjsQ