Pneumatic chucks, especially larger diameter ones have some pretty strong gripping force because the pistons have such large area in them and the ramp the jaws are sliding on is quite steep. There are some designs that have a two stage ramp that allows the jaws to open more near the end of the piston stroke but these have two limitations: You must be very careful they actually grip on the steep ramp stage and they can't be used as ID workholding chucks, at least if I remember correctly.
I was actually thinking about both of those issues as I was reading about the 2 stage ramps.
I hydro actuator has the same type valving, it's just piloted check valves.
Likely not much different than a pneu style I don't s'pose.
Think Snow Eh!