release as in allow parts to return to their starting position.
once you release the AR latch from the bevel gear, did it spin? is the piston fully forward?
you are going to find that the gears are hard to turn by hand since they are under load from the spring as well as the anti reverse latch prevents everything from spinning backwards!
you may need to open it up and determine if something isn't broken. I've had a broken tooth stuck in one of the gears before and it would lock the mechbox up.