One of the most egregious examples of poor penetration with the current generation of "hollow point" rifled slugs I have seen, was a penetration comparison between a Remington 2.75" 20 gauge 5/8 ounce rifled slug round and a Winchester #3B load on "The Box of Truth" website. In this case several layers of denim fronted a number of one gallon plastic jugs of water.
The #3B load from the 20 gauges penetrated into the fourth water jug.
The 20 bore slug fragmented and only made it into the second water jug.
Not the most scientific example but certainly unexpected!
https://www.theboxotruth.com/the-box...gauge-shotgun/