If you've caught over 400, catch another and do some terminal ballistics testing with the BB gun, bare skin and through various depths of water.
I don't know much about guns compared to most of you folks. But this reminded me of a Mythbusters show. During the show they tested the myth of people getting shot while under water, you know like in the movies where a person dives into the water and bullets go streaming past them and sometimes one of them gets hit and dies. During the Mythbuster's test it was amazing to me how much of the bullets power was lost in the first 5 feet of water depth. For most of the guns tested the bullet was non-lethal after about 5-7 feet of water depth (as tested with ballistics gel). Some of the projectiles completely disintegrated into to harmless bits once they hit the water. One particular gun and caliber was effective for several feet of depth but of course I don't remember what it was.
Perhaps if you shot the CC at the surface you could kill it (not something I would recommend for obvious safety reasons) but I doubt you will kill it in much over 3 feet of water, with a BB gun.
How about using a trot line or a trap?
