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.   

https://www.theboxotruth.com/the-box-o-truth-22-20-gauge-shotgun/

Not the most scientific example but certainly an unexpected result!

The 12 gauge slug vs. 00B result was also, shall we say, interesting.

Perhaps not definitive about all 20 gauge rifled slugs, but reflective of the exceptionally thin sidewall construction of the Remington 20 gauge 5/8th ounce rifled slug. 

The assembly of this slug round is also quite unique. Rather than seating the slug on a hard card or plastic disk, the slug under discussion is seated over a large amount of ground plastic buffer. Perhaps this is needed to maintain the relatively thin structure of the 20 gauge rifled slug under the stress of firing.

The test bed used is certainly repeatable.  Indeed, the 12 Gauge Federal Power-Shok 1 Ounce HPRS tested penetrated five one gallon water jugs. And the water jug test resulted in the classic flattened "doughnut" shape often seen in gelatin test mediums.
 
Nonetheless, I agree any speculation on relative penetration would require similar testing with a properly calibrated gelatin medium.

Such are the vagaries of empirical evidence!         

This was a simple penetration test using water jugs. Not much different than simple gelatin tests and in some ways comparable.

The water jug test had nothing to do with performance against separated hard wall barriers. 

What video?  The article only used still photographs.   

My response was a bit direct. 

I must remind myself to be wary of posting late night responses.