The invention is an adapter and a method for securing a silencer/suppressor to the barrel of a firearm. The invention incorporates a uniformly deformable spring washer positioned within a cavity within the adapter. The cavity communicates with an opening in the silencer/suppressor into which the discharge end of the barrel of the firearm is fitted. As the silencer/suppressor is secured to the discharge end of the barrel of the weapon, the uniformly deformable spring washer is deformed uniformly, locking the silencer/suppressor together with the barrel of the weapon, and preventing the silencer/suppressor from separating from the barrel.