A hammer spring assembly comprises a spring and a member operatively coupling the spring and a hammer of a firearm when the hammer spring assembly is connected to a firearm. The hammer is biased by the spring to rotate forward toward a cartridge or firing pin. The spring exerts a bias force on the member in the forward direction, which urges the member against a curved rearward surface of the hammer at a hammer contact point. As the hammer rotates rearward, the hammer contact point moves along the rearward hammer surface so as to cause a desired variation of an effective lever arm about the hammer pivot point of the bias force exerted on the hammer. Methods comprise connecting the hammer spring assembly to a firearm, or providing the hammer spring assembly and instructing a user to connect it to a firearm.