Different generations of the at-x

@spife7980 is correct. The main differences between Gen 1 and Gen 3 are how you adjust the buttstock. Gen 1 uses bolts/screws that need an allen wrench, and Gen 3 is tool less. The atx also did not come with a folding hinge or forend bridge from the factory and had to be bought separately. The atxc includes both these items, and a re designed bolt and lighter action.
 
Me personally, I’d want a pic of the set screw on the side of the rifle that you torque once you install the barrel to make sure it isn’t stripped or mangled. I’d also like to know if the comp trigger has been adjusted, as this can cause issues if not done properly, but won’t always be an issue. Other than that just your typical pics of the bolt face and rifle in general.