In late September, I wrote about the letter sent by the ATF to all federally licensed firearms dealers, explaining that it was illegal to sell guns or ammunition to state-licensed medical marijuana users. The reasoning behind this was a clause in the Federal Firearms Act that states that a person cannot purchase or possess a gun if they are “an unlawful user of, or addicted to, marijuana, or any depressant, stimulant, or narcotic drug, or any other controlled substance.” The ATF reminded gun dealers…