Tuning hatsan nova star barrel

Agree with bandg - eliminate those possibilities first. With that said.... I have a Nova in .25 cal that came with a bad barrel. I went thru a lot of testing and frustration before figuring it out. My barrel had a burr in the inlet port and the lede was poorly machined. I purchased a new barrel from Hatsan USA which turned out to be a good barrel.
 
so im checking the barrels an d now im more confused by the choice

which twist 

what is choke

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You'll still have to have it machined. These are just barrels. No crown, no leade, no transfer port, no probe oring groove, no milling for airgun receiver, or receiver oring grooves, or magazine step.



I would try polishing the barrel you have first. Then detune the gun a bit. The power adjustement is inside of the rear of the hammer. maybe a 4mm hex screw? turn clockwise to reduce power.