Knowing the mechanics of the weapons can help the shooter a lot. Knowing how your rifle works is essential. Let's take a trip inside the shotgun to understand how it works and the different mechanical solutions that can be encountered.
The percussion systems used for side-by-side shotguns are divided into two main categories: external hammer locks and internal hammer locks. In the first case, the hammers are visible and positioned on the sides of the receiver, and to shoot with each single barrel they must be cocked manually. The internal hammer guns, on the other hand, have a lever that slides in the lower part or on the sides of the receiver and which arms the hammers automatically, through the opening movement of the barrels.
Locks for external hammer guns are called forward spring or backward spring, depending on whether the "V" spring that pushes the hammer is positioned in front of or behind the hammer. When it comes to internal dog batteries, there are three basic systems. The first consists of the locks that can be placed on two side plates of the receiver, in some cases removable by hand: this is the system called “Holland & Holland”. Usually, the bar that connects the trigger to the hammer and keeps the latter in the cocking position is not unique, but is made up of two distinct pieces, which stop the hammer in two different points. If, after an accidental impact, the first trigger chain is released from the hammer, the latter travels a very short distance, after which it is stopped by the second plate. We are talking about the so-called "double safety bar" lock.
The two percussion mechanisms can equally be secured to the internal rear part of the receiver (i.e. the Anson & Deeley system). This arrangement is easily identifiable due to the absence of the side plates, even if some gunsmiths make fake folders for ornamental purposes only. In this case, however, the pins and screws through which the percussion mechanism is fixed cannot be visible on the latter. The Anson & Deeley system features slightly faster percussion and less sensitivity to accidental bumps. The only drawback of this system is that in order to obtain the space for the percussion mechanism behind the face of the receiver, the latter can be more fragile. A third system consists in mounting the hammers and ignition springs directly on the trigger bridge. This is the Dickson system.
As for the subject of the types of locks used by swinging arms, we need to take a step back in time. With the advent of breech loading, the barrels are not permanently joined to the breech, but must be able to “open” to insert the cartridges. Likewise, the closure must be solid enough to withstand a theoretically infinite number of shots, avoiding the opening of the barrels during the act of firing. Usually, in side-by-side, over-and-under and some single-barrel barrels the barrels are hinged to the breech (called the receiver) a few centimeters before the rear end, and open by rotating or tilting downwards.
As a result, the chamber swivels up, allowing cartridges to be inserted. Some appendages, called crampons, are visible between the hinge and the breech, and are inserted into special seats in the plane of the receiver. These crampons prevent the barrels from advancing during the shot and which, by interrupting contact with the action, cause the cartridge case to burst. This system is called sealing lock. Crampons generally have a notch, within which a longitudinal dowel is inserted. The latter prevents the barrels from swinging under fire (locking locking). The locking systems are of different modes: simple, double, triple or quadruple depending on the power of the gauge and the fineness of the execution. The more locking pieces there are, the harder it is to make them work simultaneously. A side-by-side usually has one or two crampons. Approximately in the middle of the rear edge of the same is visible the recess obtained within which the blocking plug is inserted. The latter can only act on the lug closest to the breech (in the case of the simple closure) or on both (in the case of the double closure). When the hole for the dowels is made in the rear corner of the first lug and in the front corner of the rearmost one, we are in the presence of the “T” closure.
A third closure, invented by the gunsmith Greener, is made behind the breeches: between one barrel and the other in the shotguns, or on the sides of the upper barrel in the over-and-under, there is an appendage or two for the over-and-under speaks of a fourfold lock) which is inserted in special notches made in the breech, with the weapon closing. A sliding transverse pin blocks this appendage by crossing it or, in the Purdey system, passing over it, so that the barrels cannot open.