Umarex ZELOS hammer

Had some time today to mess with ( up ) the zelos. Upped the regulator to 2000 psi.
Got a meaty screwdriver, set up new $33 chronograph, shot as is for stock speed.
went to adjust in 1/2 turn . Wouldn’t budge. Tried 1/2 out wouldn’t budge.
Really put some torque into it, both ways. Nothing

oh I forget screw does move 1/4 turn total then stops

did I miss something? Any ideas ?
 
Had some time today to mess with ( up ) the zelos. Upped the regulator to 2000 psi.
Got a meaty screwdriver, set up new $33 chronograph, shot as is for stock speed.
went to adjust in 1/2 turn . Wouldn’t budge. Tried 1/2 out wouldn’t budge.
Really put some torque into it, both ways. Nothing

oh I forget screw does move 1/4 turn total then stops

did I miss something? Any ideas ?
Are u sure the stock is not holding it down. Strange as mine turns so easily. There is something binding it.