The barrel-band's ability to 'clamp' is normally limited by contact with the stock or the middle sling-swivel.  Also, the pin that goes through the stock is normally long enough to prevent the 'clamped' barrel-band from moving forward.  Maybe, you have the wrong screw.  If a stacking swivel screw was used in place of the correct barrel-band screw, it would prevent the band from tightly closing on wood or its swivel.  The barrel band screw can normally be tightened to the point where the barrel-band contacts the wood or puts a lot of friction on its swivel.

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