Part 4, the bullet.
The projectile expelled from a firearm. The bullet is expected to absorb extreme heat, acceleration forces and torsional forces, reach the target at the same point every time and expand (or penetrate) predictably.
The heat generated by the burning propellant can actually melt and vaporize any exposed lead at the base of the bullet. The friction between the sides of the bullet and the rifling of the barrel can be extreme.
A bullet that leaves the muzzle at 3200 fps from a 20 barrel (M-16A2) undergoes acceleration forces of 3,073,229 FPS/s. Yes, that is over 3 million feet per second per second.
A pistol bullet that leaves the muzzle at 1200 fps from a 4 barrel (9mm) undergoes acceleration forces of 2,181,818 fps/s.
Considering that gravity is a constant force of 32 fps/s these numbers are extremely substantial.
Add to this the torsional forces of forcing a bullet to spin from 0 rpms to over 308,000 rpms (M-16) in 20 tells us that the bullet must be quite strong to keep from flying apart shortly after leaving the barrel.
Rifle bullets and pistol pullets are expected to do different things at different ranges so there are some construction differences. A rifle bullet is expected to travel hundreds of yards to the target accurately and either expand properly or penetrate properly upon impact.
A pistol bullet will generally be expected to accurately reach a target much closer (less than 50 yards generally) and perform in a like manner.
Rifle bullets can be categorized as soft point, hollow point or full metal jacket.
Soft points can be pointed, rounded or flat. Pointed soft points are intended to give a balance of aerodynamics and terminal performance (expansion). Rounded and flat point soft points are intended to be used in tubular magazine rifles so the point of one bullet does not indent and ignite the primer of the cartridge in front of it.
Hollow point rifle bullets can be pointed or rounded. Generally the pointed hollow point rifle bullets are designed to move the center of gravity (balance point) to the rear to maximize accuracy. Rounded hollow point rifle bullets are intended to give expansion upon impact.
Full metal jacket rifle bullets are generally designed to conform with international rules of war. They can have a lead core, a mild steel core, a hardened steel core or a steel insert for enhanced penetration of a protected target.
Most rifle bullets are constructed using a copper jacket and lead core. The core is forced into the jacket during construction. Some use a chemical that allows the copper jacket to bond to the lead core. Yet others use a molten lead core poured into the jacket to insure adhesion between the core and jacket.
Some rifle bullets (Barnes X-bullet) use solid copper construction with a designed hollow point to enable expansion.
Hollow point and soft point rifle bullets normally have no exposed lead at the base, the core is inserted from the front during construction. Full metal jacket bullets normally have the core visible at the base because the core is inserted from the rear.
The accuracy of the bullet in a large part depends on the quality of construction of the bullet. Run of the mill full metal jacket military bullets are made to be quickly produced and reasonably accurate. The jacket is cylindrical but not necessarily concentric. The balance may be off slightly leading to somewhat erratic flight paths.
A Match Grade hollow point rifle bullet is produced with premium components made more slowly and carefully to yield a concentric well balanced bullet that is the exact same weight as the next one so, when loaded carefully, will yield consistent results. Frequently such match grade bullets have jackets that are thinner than other designs. These thin jackets can be problematic in fast twist barrels and/or at very high velocities. Fast twist rates cause the bullet to spin at extremely high rates. Some of these bullets will fly apart when spun too fast. Likewise, very high velocities (above 3000-3400fps) can also cause these bullets to self destruct. The shooter will often notice a gray cloud a few feet from the muzzle when the bullet disintegrates. There will often be no bullet impact at all at even short ranges (25 yards).
Either of the above point shapes can be found with a flat base or boat tail. The boat tail is generally used to reduce the aerodynamic drag and increase the efficiency of the bullets flight. Boat tail bullets have a tendency to shed their cores more easily on impact adversely effecting the penetration.
Exotic bullets have become increasingly available. The previously mentioned Barnes X-bullet made entirely of copper. The combined technology Winchester silvertip has a steel insert toward the base to prevent base deformation and allow proper penetration. The Nosler Partition bullet has an H shaped cross section with separate front and rear lead cores of differing degrees of softness/hardness. Bullets with hard polymer or bronze tips to retain pointed profile until impact and then initiate rapid expansion. Bullets with soft polymer tips to allow a pointed bullet to be loaded into a tubular magazine. Bullets with specially designed profiles to maximize its aerodynamic shape.
Bullet choice depends on the intended use of the bullet. If it is intended for long range (300+ yards) accuracy and terminal performance is not an issue, a hollow point boat tail bullet is likely the best choice. If it is intended for medium range hunting on thin skinned game or varmints, a boat tail soft point is a good choice. If it intended for hunting in heavy cover (brushy, wooded terrain) with a lever action or other tubular magazine rifle, a round nose or flat point bullet would be the proper choice. If intended for hunting or self defense against large, dangerous thick skinned animals like Elk, Moose or Bears, a heavy flat based, controlled expansion bullet would be recommended. For plinking or general target shooting an economical full metal jacket would be the best choice.