the hammer on my uberti 1873 has a half moon spring loaded lever under the firing pin. if you hold the pistol barrel up in front of you you can see a flush shank head screw atop the hammer. when i removed the screw it held a spring which detents a plunger and holds that half moon lever in the up position. with the screw and spring removed the half moon is in the down position and blocks the hammer from fully traveling foward. is this some kind of safety?