Fig. 56 is the back-action mainspring, such as used in cheap made locks. These springs are also made with sear spring combined. Fig. 57 is swivel back-action with sear spring combined. [Illustration: FIGURE 54.] _Sear Springs._—Sear springs are made for right and left hand locks. The side-action or bar-lock springs are shown in Fig. 58, and the back-action lock springs in Fig. 59. In one kind of back-action lock there is used a bent spring similar to the bar-lock spring which is shown in Fig. 60. It will be observed that the lower branch of this spring is longer than that which is used in the bar or side-action locks. [Illustration: FIGURE 55.] _How to Forge Mainsprings._—If the gunsmith desires to forge his own mainsprings he must select a good quality of spring steel, as cast steel is generally too quick or fiery for springs that have as severe a duty to perform as a mainspring. Get the steel of the same thickness as the mainspring and of a width equal to the spring and the pivot that goes through the lock plate. [Illustration: FIGURE 56.] Draw the spring out carefully over a fire that has been burned enough to free it from sulphur, if bituminous coal be used, and be very careful not to over-heat the metal. Form to shape with any tools or means that may be at hand. For straight springs, as some kinds of pistol and gun-lock springs, procure steel of the thickness and width of the spring at the widest and thickest end, and draw down to the requisite width and thickness of the smallest end. [Illustration: FIGURE 57.] _How to Temper Mainsprings._—If it be a single spring that is to be tempered, heat it carefully or evenly in a fire that is well burned to free it from sulphur, or preferably in a charcoal fire, and when at a light-red heat, harden by plunging it in any animal oil. An iron pan may be used to contain the oil, and any refuse or poor oil that may collect may be used. Lard oil is good, but if oil be wanting, use common lard or even tallow. If hard, melt before using. [Illustration: FIGURE 58.] To temper the spring, remove from the oil, and hold it all dripping with the oil over a clear fire until the oil takes fire and blazes off. It is best to dip it in the oil and blaze off the second time. [Illustration: FIGURE 59.] If there are a number of springs enclose them in a piece of gas pipe to heat them, and when hot, turn them into the oil. To temper, remove them, put them in an old wrought-iron frying pan, add a little oil, heat the pan over the fire, shaking it in the meantime, until the oil takes fire and blazes off. Let the work cool without putting it in water or oil. [Illustration: FIGURE 60.] _Cheap Mainsprings for Revolvers._—Make springs for cheap revolvers from strips of sheet steel. Cut the springs so that the _length_ of the spring will be _lengthwise_ of the sheet from which it is cut, or, in other words, the _grain_ of the steel must _not_ be _across_ the spring, but _lengthwise_ with it.