Mont. Code § 45-3-104
A person is justified in the use of force or threat to use force against another when and to the extent that the person reasonably believes that the conduct is necessary to prevent or terminate the other person's trespass on or other tortious or criminal interference with either real property, other than an occupied structure, or personal property lawfully in the person's possession or in the possession of another who is a member of the person's immediate family or household or of a person whose property the person has a legal duty to protect. However, the person is justified in the use of force likely to cause death or serious bodily harm only if the person reasonably believes that the force is necessary to prevent the commission of a forcible felony.
§ 45-3-104, MCA