[MrForbes]

you can also add another cylinder, or a longer cylinder (and move the mounting points). You're correct that a larger bore cylinder might move too slowly...but then again, it might not...we had a couple of 1.5" bore cylinders on the pneumatic catapult that we used to launch the huge balls in 2008 and 2014.

but we also did a trick with pre charging them, we didn't latch them....instead, we set up the geometry so the piston had to develop quite a bit of force, before it had enough umph to launch the ball. The trick is to have the cylinder mounted so one end is just above the line from it's pivot, to the catapult's pivot.