Most airguns 'on display'in shops are 'dry fire' abused. If this was an'in the box'gun it is probably alright and should just need a good clean up. Pull a fewclean patches through the barrel and wipe away any excess oilsespecially in the compression area.
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Dieseling is usually able to be cleared up quickly by shooting a few dozen pellets if the piston seal is intact.That may not be the case since any sharp edge during assembly can ruin a piston sealthe instant it gets sliced.
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Then of course Charlie da Tunahttp://charliedatuna.com/ (http://"http://charliedatuna.com/) can give you plenty of advice, as he has seen quite a few CFX over the years.