Bartman,
I'm not a Sightron expert, but I think the way it works is that you loosen the screw and make your adjustments and then snug it back up once the adjustments are made, and go from there. As for gas being inside? I've heard they purged the scopes with nitrogen to get rid of any moisture that might be inside to prevent fogging, but I'd doubt any of them have any pressurized gas left inside them when they hit the store shelves. I may be wrong, maybe someone who knows will come along. Try posting this on the centerfire forum.
Jackie Schmidt has taken a bunch of different scopes apart and froze the inside components to use adjustable mounts. Merry Christmas!!