I see on the Montana Rifle Co web site the info on the actions as per gas handling which uses Mauser and Mod 70 features.
Years ago, when Montana Rifle announced they were going to produce actions, there was a group buy right here on the Fire (if memory serves me). At that time Pine Tree Casting (I think that is the name) were producing their actions. This is the subsidiary that cast the Ruger 77. At that time, it was described as a Ruger action built to Montana Rifle specs. I don't know it that is the case now.
