Montana

45-3-111. Openly carrying weapon -- display -- exemption. (1) Any person who is not otherwise prohibited from doing so by federal or state law may openly carry a weapon and may communicate to another person the fact that the person has a weapon.

(2) If a person reasonably believes that the person or another person is threatened with bodily harm, the person may warn or threaten the use of force, including deadly force, against the aggressor, including drawing or presenting a weapon.


Here is another good one

45-3-112. Investigation of alleged offense involving claim of justifiable use of force. When an investigation is conducted by a peace officer of an incident that appears to have or is alleged to have involved justifiable use of force, the investigation must be conducted so as to disclose all evidence, including testimony concerning the alleged offense and that might support the apparent or alleged justifiable use of force.

and

45-3-110. No duty to summon help or flee. Except as provided in 45-3-105, a person who is lawfully in a place or location and who is threatened with bodily injury or loss of life has no duty to retreat from a threat or summon law enforcement assistance prior to using force. The provisions of this section apply to a person offering evidence of justifiable use of force under 45-3-102, 45-3-103, or 45-3-104.

All the justifiable use of force laws for Montana are here

Part 1. When Force Justified - Table of Contents, Title 45, Chapter 3, MCA