This is interesting! There is definitely a conflict between state laws and federal laws because in some states, if you are a medical marijauna user, you cannot legally possess a firearm, even if it’s licensed. The ATF says that maryjane is still a Schedule I controlled substance under federal so its use is still unlawful and gun dealers cannot provide guns or ammo to anyone that they believe uses it.
Not only can a marijuana user not purchase a gun, but they also cannot ship, transport, receive, or possess a firearm or ammunition. To enforce it, the ATF has anyone applying for the purchase of a gun to fill out a form confirming that they do not use or are addicted to marijauna or any depressant, stimulant, narcotic drug, or controlled substance. Lying on the form is a felony and is punishable by up to 10 years in prison.