Is it one of those velocity knob's that you have 2 turn with the allen wrench? Or the one where you unscrew the little screw and turn it with your hand? If it is the one where you unscrew the screw then turn the hand, then see if you actually loosened the screw. If it is the other one try using a different size alan wrench and maybe dropping some oil down there to loosen it.
O and this should be in the stacked tube blowback section
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