The guns on the A-10 are awesome. If you're firing on target as little as half a second is all that is needed to deal with lightly armoured targets.
This is enabled via the Gun Pac toggle to the right of the master ARM switch. When active (and the triggered is depressed into its first stage) the plane will stabilize itself so that when you press the trigger the nose does not move up.
If you are flying with the trigger partially depressed you may notice that the plane is hesitant to move its nose up or down.
Use the master mode button to switch between the different modes.
Guns mode
DMS left / right
Used to switch between targeting modes for the guns
Weapons mode
DMS left / right does not switch between the targeting modes for the guns
The guns can still be fired
Check to see that the master arm switch is enabled
Check to see that you are either in Guns or Weapons mode by pressing the Master Mode switch