[Frank Neuperger]

Agreed on filling the larger volume taking longer. If there are restrictions in the path between the storage tank and the cylinder, you may get far less projectile height than the calculated potential energy of the compressed air. The issue is the restriction of the plumbing. The flow rate may prevent you from acheiving the launch velocity (and height) you expected. Even though a 1 inch cylinder will do less work than a 2 inch for the same static air pressure, The 1 inch ram may have a faster terminal velocity after accelerating a certain mass.

There is likely be a curve that peaks in terms of optimal bore size for given air pressure pressure, stroke length and mass to be accelerated.

Think of the extreemes... 12 inch diameter bore for 12 inch stroke would have way too much volume and fill very slow. Alternately a 0.1 inch bore would not provide enough force. Somewhere in between is the Goldilocks bore that is "just right" for the flow restrictions in your plumbing and the mass you are trying to launch.