A hand-guard and barrel nut clamping assembly for tactical firearms and other mechanical equipment that is subject to frequent or sustained vibration or shock, such as when a firearm is subjected to sustained rapid fire and/or the firearm is handled roughly. A small generally half-moon shaped anti-rotation clamping member is secured to a hand-guard support element or other suitable structure by socket head cap screws and is secured in frictional contact with components of the hand-guard mount and a barrel nut. The anti-rotation clamping member functions as a key to “tie” the barrel nut and hand-guard nut together, simultaneously preventing either one from rotating, and thus preventing inadvertent vibration or shock induced loosening of either the hand-guard retainer nut or the barrel nut. The anti-rotation clamping member is also keyed onto the front of the upper receiver by a slot into which a portion of the receiver is engaged. Alignment pins in the hand-guard support element also key a barrel nut against inadvertent rotation and further ensure against loosening of the barrel nut by vibration and shock.