When a round is fired, the bullet travels down the barrel, propelled by gas. Once the bullet passes the gas port in the barrel (a tiny hole in one side of the barrel), the gas is forced through the gas port contained by the gas block, through the gas tube, and back into the upper receiver to cycle the next round in your magazine.
There are typically 4 different lengths of gas tube: pistol, carbine, mid-length, and rifle-length.
While most calibers prefer a longer gas system to cycle smoother, certain calibers like the 300 Blackout actually prefer a shorter gas system for proper cycling.
The handguard on an AR-15 is located over the barrel of the rifle. It can come in a variety of lengths (usually 7″, 9″, 12″, 13″, 15″, and 17″), are available in drop-in or free float, can be made from a variety of materials (polymer, aluminum, and carbon fiber to name a few).
Some handguards require very few tools and know-how, while others require more extensive knowledge of AR modification and tools.
Drop in handguards will require a delta ring assembly, end cap, and either a rail-height gas block or fixed A2 front sight post.
The purpose of key screws are to hold the bolt carrier key in place.
According to Wikipedia:
Rifling refers to helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis. This spin serves to gyroscopically stabilize the projectile, improving its aerodynamic stability and accuracy.
Rifling is often described by its twist rate, which indicates the distance the rifling takes to complete one full revolution, such as “1 turn in 10 inches” (1:10 inches), or “1 turn in 254 mm” (1:254 mm). A shorter distance indicates a “faster” twist, meaning that for a given velocity the projectile will be rotating at a higher spin rate.
In layman’s terms, the lands are the raised spirals inside the barrel of your AR. The grooves are the “ridges”.
When the bullet travels down the barrel after being fired, it uses the lands and grooves to create spin (twist referred to earlier), which affects accuracy, distance, and trajectory.
The lower parts kit for an AR-15 usually contains all of the pins/detents and springs necessary to complete the lower receiver.
Some lower parts kits will omit the fire control, safety, and pistol grip – or may exchange/upgrade these items for better-than-mil-spec quality parts.
Traditionally, a complete lower parts kit contains:
- Bolt Catch,
- Bolt Catch Plunger,
- Bolt Catch Roll Pin,
- Bolt Catch Spring,
- Buffer Retainer,
- Buffer Retainer Spring,
- Disconnect Spring,
- Hammer Pin,
- Hammer Spring,
- Magazine Catch,
- Magazine Catch Button,
- Magazine Catch Spring,
- Pistol Grip (A2 style),
- Pistol Grip Lock Washer,
- Pistol Grip Screw,
- Pivot Pin,
- Pivot Pin Detent,
- Pivot Pin Detent Spring,
- Selector Detent,
- Selector Detent Spring,
- Takedown Pin,
- Takedown Pin Detent,
- Takedown Pin Detent Spring,
- Trigger Guard,
- Trigger Guard Roll Pin,
- Trigger Pin,
- Trigger Spring
The Meloniting/ Salt-Bath Nitriding (also called QPQ) process heats the barrel or bolt carrier group to 1100 degrees by dipping it into meloniting salts in liquid form.
This process and the lower temperature being used is dramatically reduced from the standard heat treatment process, giving less chance of warping the barrel, less damage to the steel.
Compared to chrome lining, the meloniting process is both a superior process and cheaper.
And talk about corrosion resistance! You could feasibly throw your barrel or bcg in ocean, come back a year later, and it will still look the same! (Please note that we did NOT just suggest that you throw your AR in the ocean).
Meloniting also gives the barrel or bcg a Rockwell hardness of between 68-72. Read: that’s stinking HARD! It’ll last longer, it’ll be easier to clean, and reduces copper fouling.
You can fire in excess of 15,000-20,000 rounds without seeing degredation in a melonited barrel. (Remember how many round we said a non-treated barrel could shoot earlier? Told you there’d be a test!)
This can double to triple the service life of the barrel. Your grandchildren will shoot out that barrel before you do!
Note: You cannot melonite a chrome-lined barrel or bcg. The chrome and melonite salts have a violent (read: explosive) reaction to each other. We’re trying to increase the life of the barrel, not shorten it!
Minute of Angle (MOA) is the term used as the standard for measuring the accuracy of a hunting rifle. You can also use minute of angle as a means of measuring the size of an animal’s target zone. In the simplest terms, there are 360 degrees in a circle, each degree has 60 minutes. The calculated distance extended to a target at 100 yards is 1.047 inches or “one-minute.” This number is just a crosshair over “one inch” and to make calculating easier, most all hunters and shooters use “one inch,” this is called “shooter’s minute of angle.” In terms of accuracy, if a hunter and his/her rifle can shoot three or five rounds and have them group inside one inch at 100 yards, then you have a minute of angle group, or a minute of angle rifle.
A muzzle brake or recoil compensator is a device connected to the muzzle of a firearm or cannon that reduces the amount of perceived recoil when the AR is fired, as well as helping to control muzzle rise after the firearm has discharged.
They are also used on pistols for practical pistol competitions, and are usually called compensators in this context.
Flash suppressors are very different from muzzle brakes! While they are both located/mounted in the same place on the AR, muzzle brake is used to reduce the perceived recoil a shooter experiences (and typically has zero to do with eliminating flash), while the flash suppressor only limits the amount of flash the shooter sees and usually does not affect recoil.
According to Legal Dictionary:
The first attempt at federal gun-control legislation, the National Firearms Act (NFA) only covered two specific types of guns: machine guns and short-barrel firearms, including sawed-off shotguns. It did not attempt to ban either weapon, but merely to impose a tax on any transfers of such weapons. Despite these limitations, it led to a precedent-setting U.S. Supreme Court decision.
In the 1930s, the United States faced a run of much-publicized gangster violence, led by such well-known criminals as John Dillinger, al capone, Baby Face Nelson, and Bonnie and Clyde. The sensationalistic aspect of their crimes convinced the administration of President franklin d. roosevelt that something needed to be done to control the spread of weapons into the general population. U.S. Attorney General homer cummings and his staff began the process of drafting recommended legislation that would achieve this goal.Cummings and his staff quickly determined that, rather than ban weapons and run afoul of the Second Amendment, they would try to tax such weapons out of circulation. As originally proposed, the NFA covered a fairly broad range of weapons, but as passed by Congress, it’s scope was narrowed to cover only “A shotgun or rifle having a barrel of less than eighteen inches in length, or any other weapon, except a pistol or revolver, from which a shot is discharged by an explosive if such weapon is capable of being concealed on the person, or a machine gun.”
The statute levied a $200 tax on each firearm defined as above, for any transfer involving the firearm. The tax was to be paid by the transferor, and to be represented by appropriate stamps to be provided by the commissioner. It was declared unlawful for anyone to sell or receive a firearm in violation of this section, and they could be fined $2,000 and imprisoned for up to five years for violating it.
While the $200 tax does not seem like much in current dollars, it represented a very large amount in 1934—in many cases the tax was more than the cost of the firearm itself. The act also required dealers of the listed firearms to register with the federal government, and also required for firearms sold before the effective date of the act, that “every person possessing a firearm shall register, with the collector of the district in which he resides, the number or other mark identifying such firearm, together with his name, address, place where such firearm is usually kept, and place of business or employment, and, if such person is other than a natural person, the name and home address of an executive officer thereof.”
The NFA did not inspire as much controversy in 1934 as gun-control acts do today, in part because of the general public perception that crime was out of control and in part because anti-gun-control groups such as the National Rifle Association (NRA) did not have nearly the strength or Lobbying power they would later have. In fact, the NRA formed its legislative affairs division, a precursor to its powerful lobbying arm, in 1934 in belated response to the NFA. Nevertheless, the NFA did result in several lawsuits claiming the law was unconstitutional, one of which reached the Supreme Court.
In Miller v. United States, 307 U.S. 174, 59 S.Ct. 816, 83 L.Ed. 1206 (U.S.Ark. 1939), two men were charged with transferring a double barrel 12-gauge shotgun in violation of the NFA. A federal district court quashed the indictment, ruling that the NFA did indeed violate the Second Amendment. But the Supreme Court, in a unanimous decision, disagreed.
Writing for the court, Justice james mcreynolds famously dismissed the defendants case with this statement: “the absence of any evidence tending to show that possession or use of a ‘shotgun having a barrel of less than eighteen inches in length’ at this time has some reasonable relationship to the preservation or efficiency of a well regulated militia, we cannot say that the Second Amendment guarantees the right to keep and bear such an instrument.” McReynolds added that “certainly it is not within Judicial Notice that this weapon is any part of the ordinary military equipment or that its use could contribute to the common defense.” He also noted that many states had adopted gun-control laws over the years.
The NFA is still in force, codified in amended form at 26 USCA § 5801 et. seq. As the first federal gun-control legislation, it set the stage for all other federal Gun Control laws, and its legacy overshadows the scope of the law and the limited number of weapons to which it actually applied.