Mont. Code Ann. § 19-8-1001

If the board finds that a member died as a direct and proximate result of injury received in the course of the member's service, a monthly survivorship benefit must be paid to the member's designated beneficiary equal to 50% of the highest average compensation of the member. If the deceased member has completed more than 25 years of service credit, the survivorship benefit must equal 2.5% of the member's highest average compensation for each year of service credit.