£800 H&k M110A1 GAS BLOWBACK RIFLE umarex VFC

Bran new not been used rally 80 shot out my back garden try set hop up. H&K M110A1 Gas Blowback Rifle (Umarex/VFC) only problem ave had its not shooting far anoth and tryed to turnd hop up up. I think its because of a improperly tuned NPAS (Negative Pressure Air System) restricting gas flow. Open to offers but not daft ones