It’s rigid by the very shortness of the action itself. It’s similiar to bending arrows that are equal in every way except for length. For an example, one is 24” and the other is 30”. The 30” arrow will be easier to bend. Since the shorter action is stiffer it will provide a better support for the barrel that's screwed into it and the barrel will flex less. I know most benchrest guns have sleeves installed over their short actions, to make them even stiffer. So, it must improve accuracy. Finally, the unbelted case design means head spacing will be on the shoulder, which is more exact than head spacing on the belt of a belted cartridge. This also increases accuracy. However, the difference will not be seen in all rifles.