I'm going to give props to @nitesite before I go any further because he was the person who talked about doing this. He has affectionately called it a TATER TUNNEL for a while now. And while I haven't used it yet, I'm looking forward to it after it warms up some. In short, I have wanted to do some bullet testing to see what kind of penetration and possibly expansion that I should expect from some of my handloads. Especially if I can compare to factory loads to get a baseline of what I should expect. I know the FBI preferred method is using ballistics gel. And I'm not going to say that's necessarily bad, but I'm not the fbi and I can't just go out and blow a bunch of money on ballistics gel. I'm not interested in finding out the temporary wound channel and other such stuff, which gel would work better for since you can see the wound channel in gel, but I am interested in penetration and expansion or deformation of the bullet at this point, and why I built a tater tunnel to test some of the 165 gr 9mm bullets to see whether or not I could/should trust them for defense, or to just use them for range fodder. My youngest son and I made this from some wood that I had laying around in the shop. While I expect the potatoes to stop the bullets faster than ballistics gel due to them being harder and more firm, if I can compare to "factory" loads, should still allow me to get a good idea of whether these will perform as well or better. The depth of the tunnel is currently 23 inches, and I can move it farther back if I need to make more room. But as I mentioned, I don't expect the penetration will be as deep as most 16" NIJ standards anyway. To make it easier to use at our range, we marked the top of the tunnel with a tape measure so we can know at a glance what kind of penetration we're getting and so I don't have to pack a ruler with us. I also stapled some denim over the mouth of the target just for good measure. And so I can draw an aiming dot on it.