 The weapon itself is cheap to manufacture but is inaccurate and prone to jamming and misfires.The FP-45 Liberator and the Deer gun are crude zip gun-like pistols or derringers manufactured by the United States government for use by resistance forces in occupied territories, during World War II and the Vietnam War.The FP-45 was a crude, single-shot pistol designed to be cheaply and quickly mass-produced.