How much damage does this exactly increase? And could the damage increase be more on weaker weapons? Not sure what happened but Winchester Rifle singlehandedly carried me through the game after picking this item up. Normally it'd take 3-4 shots to kill the early shotgun Bullet guys at early floors, but after picking it up it'd one shot almost anything, even in the Forge. The Skeleton that throws bullet beams at you took only three shots to kill?!
Well, I'm fairly certain the huge damage boost is only applied to specific weapons, seemingly single-projectile "sniping" weapons. Rifles I guess? I have noticed the damage boost on the Sniper Rifle and the Crossbow for example, while other weapons (shotguns, handguns) remained unaffected.