i like to use scrub oaks to assess penetration. there are lots of them on my farm and they are "free media." I try to find one with a 3 inch diameter, and i shoot it from whatever distance i think i will be shooting. pass thrus indicate plenty of power, as i think you would be surprised to see all the rounds a little sapling will stop. Obviously you have to use the same width and type of wood, which is why i choose oak. a pefect example is even an arrow will fully pentrate a sumac tree, but will not even sink to the end of the ferrule in oak. just my way of doing it. ballistic gel and all that other stuff is outrageously priced. also note, i am testing penetration, nothing else.