I would advise using the Accushot mount also,,,, they have never failed me yet... As for shimming,,,,, you shouldn't have any problems with the GAMO Hunter Extreme, barrel droop is usually not an issue with the GAMO rifles. RWS rifles on the other hand are known for droop and an adjustable mount is useful with them,, but the GAMO shouldn't give you any scope problems as far as windage and elevation adjustments....
Jeff