Stock assembly and recoil system for a firearm

A firearm comprising:

• a lower receiver having a forward end and a rearward end;
• a stock assembly coupled to the rearward end of the lower receiver, the stock assembly comprising:
• a receiver extension having a forward end coupled to the rearward end of the lower receiver and a rearward end;
• a butt plate adjustably coupled to the receiver extension and movable between an extended position and a collapsed position, the butt plate coupled to the receiver extension by a stock knuckle including a tubular portion received over the forward end of the receiver extension and captured between a raised collar and the rearward end of the lower receiver, and a guide portion extending from a lower surface of the tubular portion;
• and
• the stock knuckle further including an adjustment mechanism including a pivoting latch having a detent end and a biased end, the pivoting latch pivotally attached to the guide portion and pivotal about a central pivot point between a locked and an unlocked position, and a detent member carried by the guide member and forced upwardly to engage the receiver extension by the detent end in the locked position, and disengaged from the receiver extension in the unlocked position, the biased end being biased to retain the pivoting latch in the locked position.