I had a commercial bullet casting business. Naturally I needed to test the product. I tested a lot of loads fresh off the press before I loaded a boat load of them... including bought JHPs. In constructing my test area, I lugged buckets of beach sand and filled paper bags with it, all in a row. Conveniently the paper bags were 6" deep. About all JHP loads, max 357 loads, 41 mag, 45acp would penetrate into the third bag, penetration of 12-18 inches in fine beach sand. Bullets fully expanded. I got the same penetration range in LSWC ammo.
I wouldn't count on something stopping bullets without planned hardening like a steel plate.

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NRA LIFE
Reserve Officer 9yrs