The State of Montana automatically restores felons’ gun rights once they complete their underlying sentences, so long as the crimes for which they were sentenced did not involve a dangerous weapon. However, in Van der hule v. Holder, the Ninth Circuit Court of Appeals stripped those gun rights under federal statute.
Paige Griffith, Case Note, Orange Is Forever the New Black: The Right to Bear Arms Quashed for Montana Felons in Van Der Hule v. Holder, 75 Mont. L. Rev. Online 67, https://scholarship.law.umt.edu/mlr_online/vol75/iss1/13.