Looking for some input from all you guys that do lots of shooting and pattering. My son wants to do a project for school on shotgun shells. He want to do a test on three name brand manufacturer of shells and he wants to do a force = penetration on three different types of shot like copper, steel and tungsten from each manufacture of shells. He wants do show witch shot will penetrate more. I was thinking like using 20 gauge 2 3/4 # 2 or buckshot to do it with thinking it be easier to measure with less shot to weed through. I was thinking of plywood for backing but that's lot of plywood to waist , not sure but I was thinking it will take at least three layers of 3/4 at 2x2 each, and looking at doing at least three shots of each manufacturer to get a percentage. What have all you used for backing and do you thing cardboard would work or any others? Not sure what to expect on the penetration but sounds like some fun at the range shooting. Any help will be appreciated Thanks.