I should also add here that ds1 has made guns out of duplo, sticks and even cruskits before.
mine too, and in the absence of those they use their fingers. My rules are no toy guns outside the house, and no pointing them at people. They generally shoot imaginary baddies. I can't complain, I had real guns as a kid for target practice. I used to shoot tin cans of cat food at the bottom of our garden. Yet I can assure you I am not a psychopath or maladjusted in any way.