The Heavy Damped (HD) PCC Buffer Model has stiffer hydraulic dampening and stronger return spring for high stress applications. For Pistol Caliber Carbine builds that need increased shock absorption. Can be used in typical PCC carbine builds as well as short-stroke systems, and for hotter ammo. This HD model is not recommended for short barreled builds since they do not run the bolt as hard and will get more effect from the standard model. This buffer model was developed to fill the need for stiffer shock absorption which is needed on some PCC guns. If you plan to run your gun in a short stroke manner, then we recommend this buffer with our PCC buffer weight which will add mass while shortening the stroke. Many shooters feel that this buffer with the PCC buffer weight is the softest running even with a full stroke 16" carbine.