Here are the conditions and results.
-18.5'' Remington 870 barrel (no aftermarket chokes, as it comes from the factory)
-Test rounds fired from 10 feet
-FBI spec (their term) Clear Ballistics gel block
-4 layers of denim
-1429 fps average velocity
-17-25'' of penetration
Here's the video showing the test, the permanent cavity, and a discussion of the results: