RIFLES
Rifles are a type of firearm, predominantly engineered to be fired from the shoulder. Traditionally, they have a long spirally grooved barrel (Rifled Barrel) similar to the rails of a train, which are designed to spin a bullet upon firing. This enhances the bullet's stability, allowing for greater accuracy potential over longer distances. Hence, the classification "Rifle".
Rifles are a long distance solution to accurately fire a projectile at targets over greater distances. In this section you will learn the basic components of rifles, as well as the details of their particular functions. Please take a few moments and review the basics of a rifle's action, parts & terminology, and ammunition use.
Rifles can be classified under three (3) prime action groupings most commonly circulated amongst firearm owners today (depending on activity and purpose of use); Bolt Action Rifles, Lever Action Rifles, and Semi / Full Automatic Rifles:
BOLT ACTION RIFLES
Bolt action is a type of action in which the firearms bolt is operated manually in order to initiate the firing sequence. The sequence of fire begins with manually opening and closing the breech with a bolt handle (most commonly placed on the right-hand side of the rifle). As the bolt handle is pulled to the rear towards the stock, the bolt unlocks and allows the opening of the breech and a spent cartridge case can be ejected (if manually operating the bolt handle after the sequence of fire). The firing pin will then cock (this action can occur either on the opening or closing of the bolt, depending on model), and a fresh cartridge can be fed into the chamber, followed by the bolt locking in place by pushing the bolt handle forward towards the muzzle.
Bolt-action firearms are commonly seen in active practices such as hunting, target shooting and even precision long distance shooting. Compared to other manually operated firearm actions, bolt action rifles offer an excellent balance of strength, ruggedness, reliability, and potential accuracy (light weight and much more economical than auto-loading firearms), and can also be maintained much faster due to fewer moving parts. The three (3) most common bolt-action designs can be seen with Mauser systems, Lee‑Enfield systems, and Mosin‑Nagant systems.
LEVER ACTION RIFLES
Lever action is a type of action in which the firearm incorporates a manual lever (incorporated with the trigger guard) to load cartridges from storage into the chamber preparing the firearm for the sequence of fire. Lever-action rifles are generally popular amongst hunters and sporting shooters. The main drawback for a lever-action is that they can be difficult to manipulate from the prone position, especially with other advantageous actionoptions available such as a straight-pull or rotating-bolt rifle. In addition, lever-action firearms traditionally are designed to be fed ammunition from a tubular magazine, limiting the types of ammunition that can be applicable for use.
Pointed centerfire cartridges, as an example, can cause accidental discharges in a tubular magazine (the point of each cartridge's projectile rests on the primer of the next cartridge while stored). The tubular magazine may also have a negative impact on the harmonics of the barrel, which can place limits on the theoretical accuracy of the rifle.
Due to the higher rate of fire and shorter overall length of the complete rifle than most bolt-action rifles (carbine sized), lever-action rifles have remained their popularity for sporting use, especially cowboy action shooting as well as short-range hunting. An additional advantage over typical bolt-action rifles is the lack of handedness; lever-actions like pump-actions are frequently recommended as ambidextrous in sporting activities.
SEMI-AUTOMATIC RIFLES
Semi-automatic Rifles ‑ The action of semi-automatic, sometimes referred to as an auto-loading rifle, is a mechanism known as a closed-bolt firing system. These rifles are designed with mechanisms in the receiver that perform all the functions of the sequence of fire automatically. Traditional closed-bolt systems requires a cartridgeto first be chambered manually before the rifle is ready for the sequence of fire. Once a cartridge is chambered, the trigger can be pulled causing the hammer and firing pin to move, striking the primer and firing the round.
While all basic firearm actions require the action to be cycled manually before the first shot, semi-automatic and full-automatic, as well as selective-fire actions, are differentiated from other firearm actions by eliminating the need to manually cycle it after each sequence of fire. For example, to initiate the sequence of fire from a semi-automatic or a selective-fire firearm set to fire semi-automatically, the action would initially be cycled to load the first cartridge and the trigger would need to be pulled each time (once for each sequence of fire). For all other firearm's, the action requires cycling manually prior to sequencing the rate of fire. An automatic or a selective-fire firearm set to fire automatically would be able to discharge continuously as long as the trigger is held or until the ammunition storage or feeding device runs out.
These rifles are generally made from lightweight synthetic materials that make them easier to carry and manipulate.
Take a moment to study the primary parts of each rifle action so you can learn the mechanics and terminology associated with each type of rifle.
PRIMARY PARTS OF RIFLES
Bolt-Action Rifles
Bolt Handle ‑ a handle that manipulates the bolt, usually located on the right side of bolt-action rifles. Operation of this handle allows the shooter to pull the bolt handle back (towards the stock), unlocking the bolt from the breech. This motion results in the hammer or striking pin being cocked readying the rifle for the sequence of fire. Also functions as an extractor for spent cartridges to be ejected from the chamber, as well as allowing a fresh cartridge to be loaded. Pushing the bolt handle forward locks a fresh cartridge into the chamber and closes the breech.
Safety ‑ a mechanism that is toggled to provide an extra safety measure; locks the trigger, hammer and bolt from sequencing the firing mechanism of a rifle, and ensuring prevention of an accidental discharge.
Grip ‑ a part of the firearm's lower frame that is gripped by the hand, usually textured to provide additional positive traction for a firm and sure hold of the firearm.
Stock ‑ also referred to as a shoulder stock, buttstock, or even a butt. It's the rear of a rifle, traditionally attached to the receiver or chassis, and held against the shooter's shoulder when sequencing the firing of a rifle. The stock provides a means for the shooter to firmly support the device and comfortably aim. The stock also helps to manage the recoil between the receiver and shooter's body.
Butt (Recoil Pad) ‑ Commonly referred to as the "Recoil Pad", is the rear end that is pressed directly against the shooter's shoulder.
Sling Stud ‑ A mounting point to attach a sling to the firearm.
Trigger ‑ A lever that is "pulled" or squeezed to initiate the firing sequence (discharge a cartridge).
Trigger Guard ‑ The lower portion of a firearms frame (receiver) that wraps around the trigger, providing for additional protection and safety.
Receiver ‑ The receiver is designed to hold all the mechanical parts together. These parts traditionally include the trigger housing, bolt carrier group, andmagazine well.
Magazine Floor Plate ‑ Hinged metal plate located on the lower end of the receiver that can house a magazine and covers the loading port (commonly incorporated on bolt-action rifles).
Forestock - Frequently referred to as a "Fore-end", this is the forward grip of a rifle.
Muzzle ‑ The business end of a rifle (end-point of a barrel) where the projectile exits the firearm.
Barrel ‑ Simply, the discharging tube of a firearm. The tubes are meticulously engineered and bored out to provide an exit path for the discharging projectile. Once the projectile is fired, it's guided through the barrel bursting out the muzzle by expanding gas forces. Modern rifles are designed with a spirally grooved bore more commonly referred to as a "rifled" barrel.
Chamber ‑ A single chamber to the rear of a barrel where the cartridge is fed to align with the barrel for the sequence of fire.
Ejection Port ‑ an outlet in the receiver of a firearm through which the expended cases are ejected from the chamber (barrel) after a firing sequence.
Lever-Action Rifles
Bolt ‑ A sliding metal bar mechanism incorporated into a firearms receiver that positions the cartridge in breech-loading rifles, closes the breech, and assists in ejecting spent cartridges. The bolt also assists in feeding the cartridge into the chamber preparing the firearm for sequence of fire. Once the trigger is pulled sequencing the last step in firing the firearm, the bolt operates as a rear barrier ensuring gases from escaping out the back of the chamber.
Receiver ‑ The receiver is responsible for holding all the mechanical parts together of a firearm. These parts traditionally include the trigger housing, bolt carrier group, and magazine port.
Hammer ‑ A mechanism of a firearm that impacts the firing pin, initiating the sequence of fire. Once the trigger is "pulled", the cocked hammer is released and impacts the firing pin striking the chambered cartridge. This effect punches the primer on the cartridge and causes the powder to ignite and burn. The expanding gases that are caused as a result will then propel the projectile down the barrel of the firearm.
Grip ‑ A part of the firearm's lower frame that is gripped by the hand, usually textured to provide additional traction for a firm hold of a firearm.
Stock ‑ Also referred to as a shoulder stock, buttstock, or even a butt. It's the rear end of a rifle, traditionally attached to the receiver or chassis, and held against one's shoulder when sequencing the firing of a rifle. The stock provides a means for the shooter to firmly support the device and comfortably aim. The stock also manages the recoil between the receiver and operator's body.
Butt (Recoil Pad) ‑ Commonly referred to as the "Recoil Pad", is the rear end that is pressed directly against the operator's shoulder.
Sling Stud ‑ A mounting point to attach a sling to a firearm.
Lever ‑ A hand-operated lever arm in front of the trigger housing; allows the shooter to load and eject cartridges into the rifle by shifting the lever forward and back. The lever also functions as the rifles trigger guard.
Trigger ‑ A lever that is "pulled" or squeezed to initiate the firing sequence (discharge a cartridge).
Loading Port ‑ Located at the bottom of the receiver, forward of the trigger and lever on lever-action rifles. Allows the rifle to be loaded with a magazine, or manually loaded with cartridges into the internal tube magazine of the rifle (depending on the model of firearm).
Forestock ‑ Frequently referred to as a "Fore-end", this is the forward grip of a rifle.
Muzzle ‑ The discharging end of a gun (end-point of a barrel) where the projectile exits the firearm.
Barrel ‑ Simply, the discharging tube of a firearm. The tubes are meticulously engineered and bored out to provide an exit path for the discharging projectile. Once the projectile is fired, it's guided through the barrel bursting out the muzzle by expanding gas forces. Modern rifles are designed with a spirally grooved bore more commonly referred to as a "rifled" barrel. Think train rails.
Muzzle - The business end of a weapon (front end-point of a barrel) where the projectile exits the firearm.
Front Sight ‑ Located at the front end of the barrel towards the muzzle that enables the firearm to be aimed accurately while engaging the firing sequence.
Rear Sight - Located at the rear of the rifle near the stockthat enables the firearm to be aimed accurately while engaging the firing sequence.
Ejection Port ‑ an outlet in the receiver of a firearm through which the expended cases are ejected from the chamber (barrel) after a firing sequence.
Semi/Full- Automatic Rifles
Upper Receiver ‑ the upper frame of a rifle that contains and organizes all of the crucial mechanical parts, such as the bolt and bolt carrier group, forward assist, and charging handle.
Charging Handle ‑ the charging handle allows the shooter to pull the bolt carrier group towards the stock and upon release, feeds a cartridge into the chamber, hence charging the rifle for the sequence of fire. It also enables the shooter to engage the bolt catch and lock the bolt into the 'back' or rearmost position.
Forward Assist ‑ this knob serves as a backup redundancy in case the bolt does not completely seal a cartridge into the chamber. If the bolt is obstructed by gunk, dirt, dust and is not able to close properly against the back of the cartridge, the shooter can use the forward assist to "pound" the bolt forward into the fire position. This is usually NOT recommended, as it can compound a simple malfunction into something far worse.
Buffer Tube ‑ the buffer tube is comprised of the buffer spring and a weight filled buffer. The buffer tube provides the forward force on the bolt after a cartridge is discharged, allowing the bolt to chamber a new cartridge after the spent one is ejected on the rearward cycle of the bolt. The buffer spring also assists in managing the recoil between the receiver and operator's body.
Buttstock ‑ also referred to as a shoulder stock, buttstock, or even a butt. It's the rear end of a rifle, traditionally attached to the receiver or chassis, and held against one's shoulder when firing a rifle. The stock provides a means for the operator to firmly support the device and comfortably aim. The stock also helps manage the recoil between the receiver and shooter's body.
Storage Compartment ‑ small storage compartment available in certain styles of stocks. Can hold small items like batteries, compass, cleaning equipment, etc.
Rear Takedown Pin ‑ mounting pin in the rear of the lower receiver that enables the receivers to be disassembled, splitting the upper receiver & lower receiver.
Lower Receiver ‑ the lower frame of a rifle that houses crucial mechanical parts such as the trigger housing group, selector switch, manual safety, and magazine housing.
Grip ‑ a part of the firearm's lower frame that is gripped by the hand, usually textured to provide additional positive traction for a firm hold of a firearm.
Trigger ‑ a lever that is "pulled" or squeezed to initiate the firing sequence (discharge a cartridge).
Trigger Guard ‑ the portion of a rifles lower frame (receiver) that wraps around the trigger, providing additional protection and safety.
Magazine ‑ a "boxed container" (ammunition storage device) that is spring operated to hold and feed cartridges; can be fixed or detachable depending on the firearm make & model.
Magazine Release ‑ a knob permitting the magazine to be locked or released from the frame of a firearm; a function exercised through the bottom of the lower receiver of the rifle.
Magazine Well ‑ the housing that helps feed and holds the magazinein place; located on the lower receiver on most semi/full-automatic rifles.
Front Pivot Pin ‑ mounting pin towards the front of the lower receiver that enables the receiver to be disassembled, splitting the upper receiver & lower receiver.
Mounting Holes ‑ mounting points on the upper receiver, traditionally incorporated on the handguard that allow the operator to attach swivels or sling mounts.
Gas Block ‑ attached to the barrel at the point where the Gas Port is cut into the barrel. The gas block is attached at two ends, the gas port on the barrel, and the gas tube. The gas tube is designed to transport the high pressure gas that was diverted by the gas block, and channel it back to the upper receiver and into the gas tube receiving end of the bolt.
Barrel ‑ the discharging tube of a firearm. Barrels are meticulously engineered and bored out to provide an exit path for the discharging projectile. Once the projectile is fired, it's guided through the barrel bursting out the muzzle by expanding gas forces. Modern rifles are designed with a spirally grooved bore more commonly referred to as a "rifled" barrel that is similar to the rails of a train.
Muzzle - the discharging or business end of a gun (front end-point of a barrel) where the projectile exits the firearm.
Muzzle Brake ‑ a muzzle brake, recoil compensator, or flash hider is a device connected to the muzzle (Barrel End) of a firearm and redirects propellant gases to counter recoil and unwanted rising of the barrel during the sequence of fire.
Front Sight ‑ located at the front end of the barrel that enables the firearm to be aimed accurately while engaging the firing sequence. Iron sights can be folded-up or down, allowing the operator to flip them up or down when the rifle is equipped with alternate optics. Iron sights can also be zeroed for operator's distance preference.
Accessory Rail ‑ mounting rail that allows for optional accessories and tools to be installed. Two most common mounting styles are Picatinny Rails and Keymod Rails.
Handguard ‑ also referred to as a Fore-end or Forestock, this is the forward grip of a rifle. It functions as a buffer between the hot barrel and the shooter's hand.
Ejection Port - an outlet in the upper receiver of the rifle through which the spent cartridges are ejected from the chamber following a firing sequence.
Ejection Port Dust Cover ‑ metal cover over the ejection port that is spring mounted to provide extra protection from outside influences like water, dirt, dust, etc. to the internal mechanisms of the upper receiver.
Shell Deflector ‑ protrusion of the upper receiver that deflects the spent cartridges from the ejection port away from the operator.
Rear Iron Sight ‑ located at the rear of the rifle near the stock that enables the firearm to be aimed accurately while engaging the firing sequence. Iron sights can be folded-up or down, allowing the operator to flip them up or down when the rifle is equipped with alternate optics. Iron sights can also be zeroed for operator's distance preference.
Bolt Stop ‑ a lever designed to stop the Bolt Carrier Group when pushed upward by the follower of an empty ammunition storage device (magazine). This positions the bolt to be locked to the rear position so an operator can insert a new magazine or ammo storage device, push the bolt stop, which immediately releases the bolt carrier groups and cycles a new cartridge into the chamber (aligned with the barrel), preparing the rifle for the sequence of fire.
Selector Switch ‑ a thumb safety switch traditionally found on the left side of the lower receiver on most modern semi/full automatic rifles. The selector switch controls the operation of the trigger as well as the action of discharge when sequencing fire by pulling the trigger.
ACTION OF A RIFLE
The action of a rifle consists of all the moving mechanisms and parts that facilitate the loading, locking, firing, extracting, and ejection of a spent shell of a rifle and the process by which that mechanism functions through the sequence of fire. In this section, we'll take a moment to explore the basics of Bolt-Action, Lever-Action, and Semi/Full-Automatic action rifles.
Bolt Action - the bolt consists of a metal tube in which the firing mechanism is housed. The tube is traditionally designed with several metal knobs (front or rear of bolt), referred to more commonly as "lugs", which primary function is to lock the bolt in place. Manual turn-bolt designs are the most commonly thought of in reference to a bolt-action design due to the practicality of use and function.
Bolt-action firearms can theoretically achieve higher muzzle velocity, therefore, generating higher accuracy than most semi/full-automatic rifles. In a semi/full - automatic rifle, some of the energy from the charge can be directed towards the extracting & ejection of the spent cartridges as well as the loading of a new cartridge into the chamber allowing for expanding gases to escape. In a bolt action, the shooter performs this action by manually operating the bolt handle, sealing the chamber during the firing sequence, allowing for much more of the energy from the expanding gases to be directed forward. However, numerous other factors related to design and ammunition affect reliability and accuracy; well -designed modern semi/full-automatic rifles can be exceptionally accurate. In addition, a bolt action's only mechanical moving parts when sequencing fire are the actual firing pin and spring. Due to fewer mechanical moving parts as well as a short lock time, it has less chance of being off target or malfunctioning.
Lever Action ‑ These rifles have a lever hinged forward the trigger group that extends over the trigger and behind it, also serving as a trigger guard. Pivoting the lever forward towards the muzzle extracts and ejects a spent cartridge from the rifle. Pivoting it back towards the stock loads a new cartridge into the firing chamber from the ammo storage or tubular magazine housed with the forestock.
Unlike bolt action rifles that require pulling and pushing to sequence fire, lever action rifles simply require the operator to push and pull, quickly engaging the sequence of fire. Lever action rifles are commonly seen in practice amongst many hunters and competition shooters considering the quick reloading advantages as well as operating the lever with the trigger hand.
Semi-automatic Action - A self-loading rifle that fires a single cartridge each time the trigger is pulled, engaging the sequence of fire. A semiautomatic firearm uses the energy generated from the firing of each cartridge to eject the spent cartridge and feed a new cartridge into the firing chamber. This action aligns the cartridge with the barrel preparing the next sequence of fire automatically. Each trigger pull sequence fires with a single discharge; the mechanical moving parts housed inside the upper receiver extract, eject, load and chamber the next cartridge rapidly, allowing the operator to sequence fire quicker and much more efficiently. Semi-automatic rifles operate on either gas, blowback, or recoil energy generated from the sequence of fire to extract & eject a spent cartridge after a cartridge was discharged and exits the muzzle, chambering a new cartridge from storage (magazine or drum), and resetting the action; thus initiating and preparing a new sequence of fire.
The self-loading design was a successor to earlier rifles that required manual-cycling of rifles after each shot, such as the bolt-action rifle or lever-action rifle, which required the operator to manually cycle the action before each shot. The ability to automatically load the next round allowed for an increase in the sequence of fire an operator could manipulate. Semi-automatic rifles are versatile designs and can efficiently feed through various ammo storage devices and designs.
RIFLE AMMUNITION
An unloaded firearm is inert. The understanding of ammunition and its interaction with a weapon are absolutely vital to unlocking the full potential of a firearm. Rifle ammunition is larger, longer, and wider than standard handgun ammunition and is offered in many different calibers. Rifles are precision instruments, therefore, the cartridges they utilize are extremely specific when considering accuracy. Following are some essential principles concerning core ammunition components, terms and standard measurements.
Ammunition Glossary
Ammunition ‑ a loaded cartridge, usually brass or steel consisting of a primed case, propellant, and a projectile.
Armor Piercing ‑ a projectile or projectile core that may be used in a handgun intended to pierce steel armor, traditionally constructed entirely, or has a core constructed from one or many tungsten alloys (beryllium, brass, bronze, copper, depleted uranium, iron, steel), or a fully-jacketed projectile larger than a .22 caliber intended for use in a handgun with a jacket weight of more than 25% of the total weight of the projectile.
Ball Ammo ‑ refers to a full metal jacket (FMJ) cartridge; a small-arms projectile consisting of a soft core (often lead) encased in a shell of harder metal usually copper or steel.
Ballistics ‑ the science of studying projectiles. Ballistics can be the "interior" (inside the firearm), "exterior" (in the air after discharge) or "terminal" (at the brink of impact). Ballistic comparison is the attempt to scientifically match a cartridge to a particular firearm and maximize its potential.
Blank Cartridge ‑ a casing that is loaded with only blackpowder or modern smokeless powder but lacking a projectile.
Bore ‑ a firearm barrel's interior, forward of the chamber.
Brass ‑ a reference for expended or used metallic cartridge cases on the ground.
Bullet ‑ a non-spherical projectile for use in a rifled barrel; the projectile itself is expelled from a firearm.
Bullet Engraving ‑ the imprint, more commonly referred to as "Grooves", cut into the bullet by a barrels rifling.
Bullet, Full Metal Jacket (FMJ) ‑ a projectile in which the bullet jacket (a metallic cover over the nose of a bullet) encloses most of the core with the exception of the base. Usually copper or steel.
Bullet, Hollow Point (HP) ‑ a bullet with a cavity in the nose, exposing the lead core, and engineered to facilitate expansion upon impact as well as avoid excess penetration.
Caliber ‑ a term used to designate the specific cartridges for which a firearm is chambered. It is assessed by the diameter of the circle formed by the tops of the lands of a rifled barrel. It is also the numerical term included in the cartridge name to indicate a rough approximation of the bullet diameter.
Cartridge ‑ a single round of ammunition consisting of a casing, primer, propellant, powder, and one or more projectiles. A cartridge can be identified as follows:
Centerfire ‑ cartridge intended for compatibility with a pistol, rifle, and revolver that has a primer central base to the axis at the head of the casing.
Magnum ‑ cartridge or shotshell that is lager, contains more powders/weight, or generates a higher velocity than standard cartridges or shotshells for a specific caliber or gauge.
Rimfire ‑ cartridge containing the priming mixture in the rim of the base, more commonly a .22 and .22 LR.
Small Bore ‑ common term generally referring to rimfire cartridges. Mostly .22 caliber ammo used for target shooting, plinking and even small game hunting.
Casing ‑ holds the bullet, propellant and primer all together. Most casings are made of brass, but can also be found in aluminum and steel.
Jacket ‑ the envelop enclosing the lead core of a bullet.
Load ‑ the components used to assemble a cartridge or shotshell. The term can also refer to the action of feeding ammo into a firearm.
Magazine ‑ a receptacle or ammo storage tool on a firearm that holds cartridges or shells for feeding the ammunition into the chamber. Magazines present themselves in many variations, can be a box, drum, rotary cylinder, or a tube (can be fixed or removable depending on the firearm).
Nose ‑ the point, tip or head of a bullet.
Powder ‑ general term expressing the propellant inside a cartridge or shotshell. Powders also come in the following variations:
Black Powder ‑ the earliest loose grain made by crushing a solid generating a propellant, allegedly created by the Chinese or Hindus. Dates back to the 13th century, was a mechanical mixture of potassium or sodium nitrate, charcoal, and sometimes even sulfur. Commonly produces a large cloud of smoke upon discharge.
Smokeless Powder ‑ a modern-day propellant composed primarily of nitrocellulose or sometimes even combined with both nitrocellulose & nitroglycerin. Generates a small cloud of smoke upon discharge.
Pressure ‑ the force developed by the expanding gases generated by the combustion of the propellant upon the sequence of fire.
Primer ‑ the ignition component consisting of brass or gilding metal cup, priming mixture, anvil, and foiling disc. It generates a spark when struck by a firing pin, immediately igniting the propellants powder.
Projectile ‑ a bullet or shot in flight after discharge from a firearm.
Propellant ‑ the chemical mixture in which, when ignited by a primer, generates a gas. The gas will then propel the projectile through the barrel.
Reload ‑ a round of ammunition that has been assembled using already fired casings (a refurbished round).
Round ‑ one complete small arms cartridge.
Small Arms, Ammunition ‑ Military nomenclature used in describing ammunition for firearms with bores (See definition of Bore), no larger than1" in diameter.
Trajectory ‑ the path of a bullet following discharge as it travels through the air.
Velocity ‑ the speed of a projectile at any point along its trajectory, commonly estimated in "feet per second".
How does it all work together?
At the beginning of the sequence of fire, the trigger mechanism is pulled which immediately releases the stored tension of the hammer and releasing it. The hammer then strikes the firing pin, which in turn hits the primer of the cartridge and ignites the powder. The expanding gases from the powder propels the round down the barrel of the firearm and exits the muzzle creating a trajectory based on velocity.
Measuring Ammunition
Depending on the origin of its invention, ammunition is measured by the Unit of Measure (UOM) of millimeters (mm) or calibers. For example, the standard AK-47 (7.62 x 39mm) ammo originated in Eastern Europe (Soviet design), whereas the traditional 5.56 AR-15/M-16 caliber (5.56 NATO = 5.56 x 45mm) was engineered, designed, and manufactured in the USA. Ammunition is calculated and codified by the overall diameters of the bullet, rim, base, and neck. For instance, a 7.62 x 39mm AK-47 round has an approximate Bullet Diameter of 0.312" (7.92mm), a Rim Diameter of 0.447" (11.35mm), a Base Diameter of 0.447" (11.35mm), and a Neck Diameter of 0.339" (8.60mm), whereas a 5.56 X 45mm NATO round has a Bullet Diameter of 0.224" (5.70mm), a Rim Diameter of 0.378" (9.60mm), Base Diameter of 0.377" (9.58mm), and a Neck Diameter of 0.253" (6.43mm).
Popular rifle calibers such as the .223 Remington / 5.56 NATO, .30-06 Springfield, .308 Winchester (7.62 x 51 NATO), 6.8mm Remington SPC, 7.62 x 39mm, 7mm Remington Magnum, .50 BMG, .22 LR (Long Rifle), .30-30 Winchester, .300 AAC Blackout, and 5.45 x 39mm are more commonly seen and used amongst shooters today. There are a number of other variations, loads, and calibers, but these are amongst some of the more popular cartridges for rifles.
For a more thorough understanding of measuring ammunition, PLEASE refer to our How-To-Guide:
-Understanding Ammunition (Volume 1)
What ammunition do I need?
First and foremost, please refer to your firearms "User's Manual" included with purchase, and identify the manufacturer's specific instructions for the proper ammunition recommended & tested for the specific firearm make & model. If you are considering utilizing a different brand, load, or type of ammunition than the manufacturer's recommended & approved ammo, then accept the responsibility of researching the intended ammunition completely. Employing the wrong brand, load, or type of ammunition can cause severe complications with engaging the sequence of fire; such as feeding issues, firearm malfunctions, discharge problems and other severe consequences, resulting in a serious injury, damage to property, or even DEATH.