Hi, I just got one of these PC carbines a couple of days ago so I'm still trying to familiarize myself with it and don't have much room to give advise. That being said, I don't think I would want to put a wrench to it. Just a couple of thoughts... Maybe the knob is already turned counter clockwise as far as it will go, Does the forend feel wiggly? You shouldn't have to turn that knob to remove the barrel/forend. Just lock the slide back, hold the locking lever forward, rotate the barrel/forend counterclockwise, pull the barrel/forend out of receiver and see if the knob will turn then. Some one else will probably show up that is more knowledgeable than I. Good luck
Let me know how yours shoots, mine is shooting to the right about 11MOA, That concerns me.
