The demon core’s shell isn’t shielding, it’s reflective and is what causes the fission material to go supercritical. The only shielding on this gun is the lead barrel. Once the two halves are closed, the entire sphere would go supercritical. Importantly, this wouldn’t cause an explosion but would instead bathe everything around it in fatal levels of radiation as the sphere rapidly heats up and starts melting. Since the lead barrel is the only shielding, anything directly behind the barrel would receive less (though probably still a fatal amount) of radiation.
The demon core’s shell isn’t shielding, it’s reflective and is what causes the fission material to go supercritical. The only shielding on this gun is the lead barrel. Once the two halves are closed, the entire sphere would go supercritical. Importantly, this wouldn’t cause an explosion but would instead bathe everything around it in fatal levels of radiation as the sphere rapidly heats up and starts melting. Since the lead barrel is the only shielding, anything directly behind the barrel would receive less (though probably still a fatal amount) of radiation.