i dont know about scottish law but english law states if it is under 12 pounds per foot(thats 300foot per second) and cannot fire fully auto it is in the same classas an air rifle and u dont need a licience.
well strictley speaking nxl is not full auto you hve to get your gun to a certain rate of fire before it will go auto and thats just a way of getting round the full auto clause.
Dude, just wrapp it up well, put recipients name and address on it, take it down to the postie , ask for either 1st class recorded, or special delivery(which ever is your preference) and hand over your cash and package.