It seems obvious to me that you're intending to create ricochets - controlled and contained ricochets. I can't see where this would be a problem as long as your angle is carefully chosen in order to create safe deflections. Obviously one would also have to be careful to insure that the deflected bullets could not encounter other hard objects or surfaces which might create dangerous secondary deflections. As for the thickness of metal needed to avoid deformation, I don't know for certain but think- based on some experience- that 1/2", even if it isn't the hardest steel, should work for a deflection plate. You might test some smaller pieces first to be sure. (And shoot them with the fastest, not necessarily the hardest or heaviest bullets you have. Speed creates penetration when metal is the target.)
