i have a gibson tune o matic and my a string is still flat and i moved the saddle all the way toward the neck that it could move
Which way is that particular saddle facing? i.e. does the ramp face the nut or the back of the guitar?
ramp faces nut
Turn the saddle around. There is a little 'C' clip that fits into a slot on the adjusting screw. Use something pointy and small to pop it off. Put your hand completely over it to prevent it from flying away. The screw can then be removed and the saddle reversed. Put the screw in and the clip back on carefully and you should be good.