Im currently designing a feather pneumatic axe which uses a modified top of a ram and toothed round bar for the piston.

Using the crank style, you will never be able to go full 180 as the ram piston will want to pull horrizontally to itself and will jam the arm as it cant force the rotate. It will work as long as you dont make it go full 180. It will put itself under alot of stress as it nears the '0' and say '270' degree mark, and will also - IIRC, it will loose speed as it approaches the max and min points of its rotation.

rack and pinion are the way to go for full power along the whole of the stroke.