Weapon laws (Title 45-8-3)
Montana does not have gun registration, licensing, or owner permits. There is no assault weapon ban or magazine capacity limitations. Private gun sales are legal. Open carry is legal and concealed weapon permits (CCW) are shall issue. Permits are generally not required outside of city/town limits.
Permitless concealed carry
It is legal for a person who is outside the city/town limits or the confines of a logging, lumbering, mining, or railroad camp or who is lawfully engaged in hunting, fishing, trapping, camping, hiking, backpacking, farming, ranching, or another outdoor activity in which weapons are often carried to carry a concealed firearm, 45-8-317(i).
Concealed carry is illegal in portions of a building used for state or local government offices and related areas in the building that have been restricted, 45-8-328(a). Local governments may prohibit carrying of concealed or openly carried weapons to a public assembly, publicly owned building, park under its jurisdiction, or school (and many do) 45-8-351.
No guns signs
No guns signs do not have the force of law on private property. Failure to leave or disarm would only be trespassing. Banks and establishments that serve alcohol, which may be posted, are regulated separately. Hotel owners are prohibited by law from banning firearms, 70-24-110.
You may not carry a concealed firearm a in an establishment that serves alcohol on the premises (bars and restaurants), 45-8-328. It is illegal to carry a concealed firearm while under the influence of an intoxicating substance, 45-8-327. This does not apply to open carry, however many establishments are mistaken about the law.
Concealed carry is prohibited in a bank, credit union, savings and loan institution, etc. during normal business hours, except when using a drive-through, ATM, or depository, 45-8-328. This does not apply to mall or grocery stores with bank kiosks unless one goes into the actual banking area. This does not apply to open carry.
Firearms are prohibited in school buildings except that school trustees may give permission to carry, 45-8-361. Parking lots and outside the school are not covered by this section. 45-8-351 allows local governments to prohibit firearms at schools as well.
Campus carry (colleges and universities)
No specific state law prohibits firearms on college or university campuses, but educational authorities ban firearms and a bill to allow concealed firearms on campus failed in the 2015 legislature.
There is no law prohibiting loaded or unloaded firearms in vehicles. Unlike other states, there is no wildlife regulation on loaded long-guns. Weapons cannot be concealed upon the person within city/town limits (see permitless carry).
It is illegal to carry a firearm on a train unless the weapon is checked as baggage, 45-8-339.
There is no specific law prohibiting firearms in airports, however local governments can ban firearms in public airport buildings 45-8-351.
It is legal to carry a concealed firearm at one's own premises (private property; land), at one's home, or one's place of business without a permit, 45-8-317(j).