Abstract: A tubular adapter (12) is clamped onto the muzzle (16) of a firearm (18). The adapter (12) is axially split where it surrounds the muzzle (16). A clamp ring (38) surrounds fingers (44) which are between the splits (28) and squeezes the fingers (44) diametrically inwardly into tight clamping engagement with the muzzle (16). The clamp ring (38) is made from a material that shrinks when it is heated. The adapter (12) includes external threads (20) and axial grooves (64) formed in the threads (20) which are spaced circumferentially about the adapter (12). A tubular weight member (14) is attached to the adapter (12) by internal threads (26) which mate with the external threads (20) on the adapter. One or more detent balls (46, 48) carried by the weight (14) enter into the grooves (64) and serve to lock the weight (14) into set positions on the adapter (12). The detent bails (46, 48) and grooves (64) provide for an axial position adjustment of the tubular weight (14) in discreet increments.