On the hanging of the swivel or stirrup depends the smoothness of play of the mainspring. On the placing of the hole for the sear-pin depends the sweetness of the sear operating on the tumbler. On the pitching of the sear depends the cutting of the notches of the tumbler, and on the formation of the first notch depends the liability of the lock catching at half-cock when the trigger is made to be easily pulled from the full cock notch. On the formation of the half-cock notch depends the safety of carrying the arm at half-cock. _The Back Action Lock._—There are various forms of gun locks, and each form has its admirers. The back action shown in Fig. 43 admits of the arm being put together more strongly and securely than any other plan. Other advantages claimed for it are that the mainspring can be made longer and will therefore be less liable to break, and by such length has a smoother working motion to the hammer. As the lock plate is almost entirely surrounded by the wood of the stock, there is less liability of wet getting into the interior, and this may especially be the case as the hand, in carrying the gun, covers some portion of the lock. [Illustration: FIGURE 43.] _The Bar Lock._—This lock, Fig. 44, is so called from a bar formed at the breech end of the barrel, and to this bar the lock is fitted. The great advantage of this lock is that it admits of the stock to be so shaped that the grasp of the hand naturally tightens as the gun is raised to the shoulder. The objection raised by some to this lock is that it is more pervious to wet than the back action lock. This lock possesses the advantage of having an arm of the tumbler so made that by the swivel or stirrup being hung upon that when the lock is at full cock the weight of the spring force is lessened by the arm acting as a lever to bring the moving force in the immediate vicinity of the axis on which the tumbler turns, and when the spring is bringing the hammer down on the nipple, increasing that force by divergence. It is sometimes called the Full Bar Lock. [Illustration: FIGURE 44.] _Side Action Lock._—In Fig. 45 is shown another form of lock, commonly called a side action. The mechanism and arrangement is similar to the full bar, but it has a shoulder that fits up to the barrel. If the gun be fitted with a plug or cylinder a suitable half round recess is cut in this shoulder to receive the plug. [Illustration: FIGURE 45.] _The Wesley Bar._—The Wesley bar shown in Fig. 46 differs from the common bar lock by being of different shape at the fore end, and this end does not fit up to the barrel like the bar lock. By the wood almost surrounding the plate, the interior is pretty well protected from wet. It has the same merit of the stock being so shaped as to tighten in the hand when raised to take sight. This lock has one objection, the wood between the lock-plate and barrel has to be cut so thin that the recoil of the gun is very apt to break and splinter it.