The AR-15 Rifle and 80% Lower Receiver
What is a lower receiver? A lower receiver is equipment that has and holds in place all the components needed for the proper operation of an AR or M16 rifle. These components are grouped as follows:
The fire control group: As the name suggests, these are the components that work in the firing compartment of an AR-15 and include the trigger and pin, hammer plus the dis-connector. They are what fire the gun when a user makes a pull to release the hammer.
Selector switch: the selector switch does just that, it switches the modes of the AR-15 from safe to fire or to automatic if you are dealing with Title 3 weapons. The selector switch comes in both ambidextrous and standardized right hand switch.
The bolt catch: in the lower parts kit is the bolt catch, a component whose function is to prevent the traveling of the bolt whenever one has an empty magazine, with the result being it getting pushed upwards.
Magazine release: the magazine release does what its name suggests; it releases the magazine and locks it in place. It is also another lower parts kit item.
Magazine well: the magazine well is where the magazine is inserted and is a lower receivers physical part. Some manufacturers, to ease magazine insertion, make flared magazine wells, though this is not a military standard requirement.
Takedown pins: takedown pins enable the user to take out an AR-15’s upper receiver for replacement with one of a different caliber or for maintenance purposes. They allow for a lot of the versatility witnessed in AR-15’s.
Handgrips: the part you hold when firing an AR-15. Handgrips can be customized as per individual taste and preference.
Upper receiver: contains the components needed for the successful firing of a round(s) including the bolt carrier group.
Buffer Assembly: also known as the lower receiver extension, it includes the buffer, the recoil springs and an extension tube.
The 80% lower receiver
The term 80% lower receiver is an industry term for an incomplete lower receiver milled by the manufacturer to 80% completion. By BATFE standards, for a lower receiver to be termed as a 80%, it should have no fire control group holes nor pockets drilled or cut out respectively. By federal law, for a 100% milled AR-15 lower, be it stripped or complete, the buyer has to have been licensed or be a holder of a federal firearms license or transact with a federal firearms licensed dealer to do an ownership transfer of a lower receiver from a dealer or manufacturer. When dealing with an 80% lower, however, no registration is necessary.
Types of lower receivers and how they are made
There are two types of AR-15 lower receivers namely, stripped and complete lower receivers. The stripped lower receiver is one that comes with the proper markings and is completely finished, they, however, do not come with any of the other components and its transfer has to be through the federal firearms licensing department. The complete AR-15 lower receiver is termed complete because it comes with all the components (handgrip, fire control group, stock, buffer assembly, lower parts kit etc.) it is the most preferred if you want to do your own AR-15 build.
Forged, billet or cast lower receiver- what’s the difference?
The main similarity among the three is that all are made from aluminum. The methodology involved is what brings the difference.
Cast 80% receiver
This simply means that the lower receiver is molded from molten aluminum, which is then cooled to form the desired shape of your AR-15 lower receiver. Molten aluminum gets poured into a mold, giving it the desired AR-15 lower receiver shape, it is then allowed to solidify and the resultant cast gets taken out of the mold. Finishing is then done through a CNC machine. It is the cheapest of the lower receivers but has garnered bad market reputation, due to poor workmanship by manufacturers; however a well-made cast 80% receiver is as good as any other type of lower receiver and will be suitable for all AR-15 application.
Billet 80 % lower receiver
The billet 80% is formed out what is called a bar stock, which is a block of solid extruded aluminum. Extrusion in this case refers to having the aluminum formed into desired shape by being rolled amidst two rollers. A piece of this extruded aluminum block is then cut into desired AR-15 lower receiver shape by a CNC machine. Billet 80% lower receivers have the most aesthetic appeal due to the fact that the CNC machine can cut the billet aluminum to produce various shapes with fine geometric designs that have fine lines.
Forged 80% lower receiver
Forged 80% aluminum lower receivers is used in general referrals to the material that gets forged into a specified or desired shape. Forging an 80% aluminum lower receiver needs application of compressive forces, to hammer the aluminum in already forged dies so that it takes the already set intermediate dimensions specified for that particular lower receiver. The CNC machine then does the finishing of the forged aluminum after it has been made into the raw initial shape.
Forged 80% aluminum lower receiver s are considered the strongest by metallurgists, this is because due to the compressive pressure applied its manufacture process, the material grains tend to follow the shape of the forged part thus resulting in a continuous character in all the material grains.
The 80% lower receiver for AR-15 rifles are not illegal, however, it’s important to know your local laws. Luckily, 80% lowers offer a lot of creative space for those who would like to have their own custom made AR-15’s that fit their preferred taste. Make sure to consider material quality, since cast, billet and forged lower receivers come in varied strengths, (forged receivers comes in two aluminum types: 7075-T6 with tensile strength of 74 and also 6061-T6 with a strength of 38, billet receivers come in 7075-T6 with 77 tensile strength and 6061-T6 with 38 tensile strength).