A lot of SAA style guns originally had a pointed firing pin attached to the hammer. Some of these were incapable of lowering the pin between the chambers in the cylinder (firing pin doesn't actually go through the frame during normal conditions. BUT, if the back of the hammer was struck a solid blow, like a stirrup falling on it from a saddle horn, or the pistol falling out of the holster onto the ground and hitting the hammer first it could force the the hammer and therefore the firing pin ahead through the frame and into a waiting primer). Bang, an accident. With those guns, 5 in the cylinder made sense. With a transfer bar, six is not an issue. - dan