I'm was getting some pretty big numbers out- but I realised I was using the diameter not the radius. I just wanted to check I hadn't missed something else daft!

Calculating force at the tip of a flipper:

Ram is 3.94 inches diameter
=12.19 InchSquare

Gas pressure 1000psi
1000*12.19 = 12 190 pounds of force
Which is 5529kg

Say I lose half through inefficiencies:

2500kg at the ram

If the ram is 10cm from the fulcrum and the tip of the flipper is 1m away there is a 10:1 reduction so

2500/10= 250kg @ tip

Sounds reasonable to me. Can anyone confirm?