To test in wet paper I tie a bundle of paper together with twine leaving plenty of slack because the paper will expand. The only purpose of the twine is to make the resulting bundle easier to handle. I used to use newspaper but those are harder to find these days so I use magazines. I put a bundle in a drywall bucket and fill it with water then let them soak at least a couple hours and I like to do it overnight. Then I put that block out at 25 yards and shoot into it. Low powered guns like my Prod and P35-177 will penetrate through less than 10 magazines with about 80 pages each. My guns in the low 30 fpe range will go through more, of course, but a stack of 20 magazines will stop even my 25s at a little over 40 fpe. If you use an expanding projectile they won't go as deep but will make a wider hole. I may use 25 or 30 magazines next test since I want to include my now ~50 fpe 25 caliber.