I use a bit of old roughed up conveyor belt rubber wrapped around the cylinder and clamped in the vice. that way you dont run the risk of squashing the cylinder or scoring it. I then clamp a couple of bits of hardwood onto the trigger block and rap it hard with the hammer.. sometimes you just need a sharp blow to loosen it... squirt some acetone up inside the trigger and try and clean out any visible gunk, then squirt in some light oil.. that way if the spring end is all gunked and stuck inside the block, it might get it moving.. it could be a bit of friction caused by that, as well as the block being stuck.

another good thing to use prior to whacking things is a penetrating oil.. ive had success with paraffin and 40w mixed, everyone has their own recipes for loosening oils.. might be worth giving the joint a wee soak and get some up inside the trigger