Many of the most crucial components on an AR-15 are held and protected by the upper receiver (often referred to as an “upper”). There are many different types of uppers on the market, and knowing the distinctions between them is critical when making or purchasing an AR-15.

You may be perplexed by the several AR-15 receiver types if you are new to the world of the AR-15 rifle. Comparing a receiver to the chassis of a car is one method to obtain a better grasp of what it accomplishes. All of the important AR-15 components are integrated into the receiver, just like a chassis. The AR-15 receiver is made up of two parts: upper and lower, with the latter being the legally regulated and serialized section. In this article, we’ll look at the several varieties of AR-15 upper receivers, such as the AR-15 A1, A2, A3, and A4.

A1 Upper

The A1 is the first iteration of the AR-15 upper receiver. The A1 was developed in the 1960s and placed on M-16 A1 rifles used by soldiers in Vietnam. A light profile barrel, forward assist, and a fixed carry handle are all key A1 characteristics. A flip rear sight is also available, which adjusts for windage but not elevation. Short- and long-range apertures are also available on the rear sight. The A1 has a twist rate of 1:12. In general, the AR-15 A1 upper allows for accurate fire from a distance of about 450 yards.

A2 Upper

In the early 1980s, the A2 upper was launched as an enhanced version of the A1. The A2 has a fixed carry handle and a forward assist, just as the A1. The A2’s rear sight, on the other hand, is more sophisticated, with elevation (usually up to 600 yards) and windage adjustments. The A2 also has a heavier barrel than the A1, as well as rounder handguards and a left-handed brass (as opposed to the triangular-shaped handguards of the A1). The A2 has a twist rate of 1:7 or 1:9, depending on the manufacturer.

A3 Upper

The A3 upper receiver has a removable carrying handle and a flat top design. An A3 upper may be fitted with either a Picatinny or a Weaver rail to serve as a mounting platform for scopes and other attachments, depending on the manufacturer and type. The feed ramp on the A3 also has forward assist and rifle cuts. Some A3 versions have a “high-rise” arrangement, which raises the base upward for better scope placement.

A4 Upper

The A4 is a flat top upper receiver, like the A3, and its design and construction are quite similar. The key difference between the A3 and the A4 is that the latter contains M4-style feed ramps to supplement the feed ramps found on an M4 barrel.

The main distinction between AR-15 uppers is whether they have a flat top or a carry handle.

The forward assist button is another important aspect. Some uppers have them, while others lack them. It’s debatable whether this button is truly necessary for civilian use, but keep in mind that they’re present on all military M16 and M4 rifles for a reason: pressing the forward assist button ensures that the bolt is fully seated.

Upper Receiver Construction: Forged, Billet or Cast

Upper receivers are available in a variety of metals, although aluminum is by far the most popular. The upper’s structure is governed by the manufacturing procedures utilized in addition to the material used.


Uppers made of forged metal have the optimal grain structure or orientation, resulting in the best combination of mechanical attributes such as hardness, fatigue limit, specific weight, and others, but they are denser and heavier. A forged upper is made by “forging” (hammering) the upper into the desired shape, and then finishing it on a CNC lathe.


The billet receiver is created by CNC machining a solid lump of metal until it reaches the desired form. Billet metal has mechanical qualities comparable to forged metal, although it is less dense and lighter at the sacrifice of a little strength.


Cast metal is the lightest of the three materials, but it also has the least amount of strength. However, because it is generally the lightest upper, cast is occasionally “good enough.” Uppers are cast by pouring molten metal into a mold (sometimes called “die casting”). After that, a CNC is usually used to conduct some finishing work.

Stripped vs Complete Uppers

A stripped upper consists just of the upper receiver — it’s essentially a solid piece of metal. The ejection port door and the forward assist button will be fitted on a finished upper. “Complete upper assemblies” are also available, which contain the entire upper as well as the charging handle, barrel, handguard, and potentially the bolt carrier group.

The stripped lower is essentially a single portion — the upper receiver. There will be a few additional components in a “full upper.” A complete upper assembly is a complete upper-half of an AR15 rifle that merely needs to be attached to a bottom receiver and fired.


When selecting an upper receiver, you should prioritize quality. You may end up with an item that is not only dysfunctional but also possibly harmful if a business ignores quality control or quality assurance stages. The bolt-carrier might become stuck if tooling markings are left in the receiver. Gas tube holes that aren’t correctly positioned can render a pistol useless. Oversized barrel extension holes allow for wobbling in barrel mating, putting stress on the barrel nut or worse. Allowing a firm to utilize you, the customer, as quality control in the name of cutting costs for lower pricing is not a good idea.

In today’s market, there are a variety of upper receivers to pick from. There are various variants available, whether it’s a full upper with barrel, gas system, and bolt-carrier group, or a stripped upper for a buyer to modify.

Given the upper receiver’s responsibilities, conduct your research and pick the finest AR-15 upper receiver that fits your intended function, money, which may entail saving a little longer to buy the right component, and desired appearance.