Owning a gun while being a cannabis user is illegal, even though the law is rarely enforced.
However, if you are employed in the cannabis industry, possession of a firearm triggers a Federal 5 year mandatory minimum sentence
United States Code Title 18, Section 922(g) makes it unlawful for certain individuals to ship, transport, possess or receive any firearm or ammunition with the required interstate commerce nexus. Prohibited classes include convicted felons, fugitives from justice, unlawful users or addicts of controlled substances (paragraph 922(g)(3)), mental defectives, illegal aliens, dishonorably discharged servicemen, and persons who have renounced their U.S. citizenship. The penalty provides that a person who “knowingly” violates this law “shall be fined as provided in this title, imprisoned not more than ten years, or both.”
Under the Gun Control Act of 1968, any “unlawful” user of a controlled substance is prohibited from purchasing or owning a gun. Because marijuana is a Schedule 1 controlled substance under federal law, the U.S. government maintains that there is no way to use cannabis lawfully.