CHARACTERISTICS OF SMALL ARMS

LEARNING OBJECTIVES: Define the term small arms. Explain small arms nomenclature. Discuss the eight steps in the small arms cycle of operation.

Strictly defined, the term small arms means any firearm with a caliber (cal.) of .60 inch or smaller and all shotguns. Since there are no .60-cal. weapons in the Navy, all pistols, rifles, shotguns, and machine guns up through .50 cal. are small arms. For maintenance purposes, grenade launchers have also been included in the category of small arms. Such weapons are carried or mounted aboard ship for certain watchstanders and members of the ship's internal security force.

Small arms intended for match competition (match conditioned) are not covered in this text. They are not repairable at any level other than depot, such as the Naval Weapons Support Center, Crane, Indiana.

The majority of small arms are procured from the Army and issued by the Navy to its field activities and the Fleet. Maintenance on these small arms is performed in accordance with the applicable maintenance requirement cards (MRCs), but all other information (operation, troubleshooting, parts lists, etc.) is normally found in Army technical manuals (TMs) and field manuals (FMs). FMs and TMs list the spare parts, special tools, and organizational maintenance procedures for a weapon. The FM is the operator's manual and is intended for personnel in the field who must keep the weapon firing. Indexes of Army FMs and TMs are printed in Army pamphlets 310-3 and 310-4, respectively; OP O also lists TMs, FMs, and OPs pertaining to small arms.

Before we begin the study of the individual weapons, let us examine some of the quirks in small arms nomenclature (names of the parts). Generally, terminology pertaining to the weapons themselves is fairly standard because the Navy has adopted most of the Army's system of identification. For example, the Army used the letters M and A instead of the abbreviation Mk (mark) and Mod (modification), This means that "Carbine M1A2," in Navy language, is "Carbine Mk 1 Mod 2."

The diameter of a shotgun's bore is referred to as the gauge of the shotgun. Gauge (with the exception of the .410 shotgun) is not a measurement of inches or millimeters. Instead, it is the number of lead balls of that particular diameter required to make a pound. For example, if you measured the diameter of a 12-gauge shotgun's bore, you would find it to be 0.729 inch. If you were to make a number of lead balls of this diameter and weigh them, you would find that 12 of them make a pound.

So the larger the bore of a shotgun, the smaller the gauge number. A 16-gauge shotgun has a smaller bore than a 12-gauge.

CYCLES OF OPERATION

In every weapon, there is a cycle of operation. This cycle is a group of actions that take place upon the firing of one round and occur before the firing of the next round. In the automatic small arms currently used by the Navy, the sequence or manner of accomplishing these actions may vary between weapons of different design; however, they are always performed.

There are eight steps in the cycle of operation; they are shown in figure 8-1.

Feeding

Feeding places a round in the receiver just to the rear of the chamber. In its simplest form it amounts to putting a cartridge by hand in the path of the device that will chamber the round. Most often, feeding is accomplished by a spring-loaded follower in a magazine.

Magazines have a limited capacity and cannot sustain the continuous rate of fire required by machine guns. Therefore, machine gun ammunition is belted,

Figure 8-1.-The small arms cycle of operation. 

and the rounds are fed to the rear of the chamber by cam and lever action.

Chambering

This action is required to ram a new round into the chamber. Again, in its simplest form, this amounts to placing the round there by hand. In military weapons, chambering takes place as the forward moving bolt strips the round from the feed mechanism and forces it into the chamber. The bolt closes on the cartridge and the extractor snaps into the extracting groove machined around the base of the cartridge case.

Locking

Locking holds the bolt in its forward position for a short period of time (after firing) to prevent the loss of gas pressure until unlocked by other forces. For low-powered weapons, it is possible to seal the breech for a short time by merely increasing the weight of the bolt. The bolt does start to move upon firing; but, if sufficiently heavy, it will not move far enough to release the gases until their pressure has been satisfactorily reduced. This method is used by submachine guns and other straight-blowbackoperated small arms, such as the .22-cal. rimfire autoloading pistols.

Firing

Firing occurs when the firing pin strikes the primer of the cartridge.

Unlocking

Unlocking occurs after the firing of the round. Actions for unlocking are just the reverse of those required for locking, For most rifles, the first movement of the bolt is a rotating one, disengaging the locking lugs.

Extracting

Extracting is the process of pulling the empty case back out of the chamber. The extractor (normally a small hooked piece of metal encased in the bolt) snaps over the rim of the cartridge case when the round is chambered. As the bolt moves rearward after firing, the extractor hauls out the empty brass.

Ejecting

It is not only necessary to pull the cartridge case out of the chamber, but also to throw it free of the receiver. This action is called ejection and is created by placing a small projection on one side of the receiver so that, as the bolt and case move to the rear, the case will strike the projection and be expelled from the weapon. This method is used in the .45-cal. pistol. Another method of accomplishing this step is to incorporate a spring-loaded ejector in the face of the bolt. In this arrangement, the case is flipped from the weapon as soon as its forward end clears the chamber. This method is used in the M14 rifle.

Cocking

Cocking is the retraction of the firing mechanism (firing pin and hammer) against spring pressure so that there will be sufficient energy to fire the cartridge in the next cycle of operation. The firing pin, hammer, or, in some cases, the bolt itself is held in a cocked position by a piece called the sear.

Again, firing is initiated by squeezing a trigger. This movement trips the sear, releasing the firing mechanism (firing pin, hammer, or in automatic weapons such parts as the bolt group or slide), causing it to move forward with enough force to discharge the round.