What very dense malleable metal is used in plumping solder bullets and shields against radiation?

The metal you're referring to is lead. Due to its high density and malleability, lead is commonly used in Plumbing solder, as well as in the production of bullets. Additionally, its ability to effectively shield against radiation makes it valuable in various applications, such as protective barriers in medical and nuclear settings. However, due to health concerns associated with lead exposure, its use has become more regulated in many industries.