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Top Questions About Rifle Uppers, Answered

Top Questions About Rifle Uppers, Answered

Posted by MCS GEAR UP on Mar 16th 2023

As you may know, many modern sporting rifle (MSR) platforms like the AR-15 do not consist of a single receiver or frame, unlike the vast majority of handguns, rifles and shotguns.

Instead, these platforms consist of both an upper and a lower receiver, which must be built out and joined together in order to create a functioning rifle.

Some build their own rifles at home and save time and money buying assembled uppers or upper assemblies instead of putting them together piecemeal.

We rounded up some of the top questions from the web and compiled the answers here.

What Is an Upper Receiver?

The upper receiver is an essential component of an MSR like an AR-style rifle that contains the bolt carrier group, charging handle, barrel, and handguard and which connects to the lower receiver via the take down and pivot pins.

What Is the Difference Between a Stripped Upper and an Assembled Upper?

If you’re considering a home build rifle project, sooner or later you’ll come across the terms “stripper upper” and “assembled upper.” These are similar but not the same.

A stripped upper is simply the machined aluminum upper receiver itself, without any of the other attachments or parts necessary to complete the build.

An assembled upper (sometimes called a complete upper) comes with most if not all of the parts (and hardware) necessary to attach to the lower receiver and those to complete a functional rifle.

                            assembled upper

Why a Stripped Upper?

In a word, customizability. Though it takes more planning and work to complete a rifle build with  a stripped upper because you will need to but all of the parts piecemeal, since you’ll have to put it together yourself, you can make very granular customizations along the way.

The Flipside: Why an Assembled Upper?

The exact opposite of customizability - convenience. If you complete a home build rifle project with an assembled rifle upper instead of a stripped upper and parts, you can save time, effort, and potentially even money during the process. Assembled uppers are basically ready to “plug and play” and come with most if not all of the parts you need to complete the build.

What Parts Does an Assembled Upper Come with?

Just what parts an assembled upper will come with will depend entirely on the package. Some assembled uppers come with more parts than others; others will come missing important components that you’ll need to add yourself.

As a for example, please see the following AR-15 upper receiver from our collection. It comes with:

  • The upper receiver itself
  • A 7.5” 5.56 NATO barrel
  • An M-LOK rail system handguard
  • A charging handle and forward assist
  • An ejection port cover
  • A gas system (tube and block)
  • And a birdcage muzzle brake

As you may have noticed, this assembled upper does not come with a bolt carrier group so that is something you will need to get to complete the build.

                     assembled upper

Other upper assembled may not come with charging handles, forward assists, or ejection port covers, so make sure you read what each comes with before buying.

Can You Buy an Assembled Upper Online?

The lower receiver is the part of the firearm that is serialized and thus considered to be a “gun” by the ATF. The upper receiver, however, is not serialized and therefore is not considered to be a firearm, proper.

As a result (and like barrels, handguards, trigger groups, and most other gun parts) you can purchase an assembled upper online, and no paperwork, background check, or FFL transfer is required. This is one of the main reasons that some people choose to purchase assembled uppers for their builds; convenience.

What BCG Should I Pair with My Rifle Upper?

That depends on the sort of performance you expect from the rifle and how advanced you want it to be. It also depends on how much you want to pay.

The first AR-15 rifles were made with hard chrome BCGs and current mil-spec BCGs are phosphate coated. Phosphate-coated BCGs are relatively affordable and offer good performance, but can be a little harder to clean and require the use of more liquid lubricant. They’re also non-reflective.

Advancements in technology have resulted in the development of newer, better BCG coatings that offer superior permanent dry lubricity. Examples such as black nitride, nickel boron, and even titanium nitride, which has a slick gold coloring.

These advanced BCG coatings are substantially more expensive than phosphate coatings, but they also offer superior hardness and permanent dry lubricity, which means less liquid lubricant is needed for cleaning. It also makes them easier to clean in the first place.

This is a topic we have covered at length in the past. For more information about the different types of BCG coatings, please consult the previous link to our blog on the subject.

Will Upper Receivers Need to Be Serialized?

According to the ATF, upper receivers (which are not currently required to be serialized) will still not need to be serialized in the future; the only part that needs to be serialized is the lower receiver.

Is It Cheaper to Buy or Build an AR Upper?

That depends on the package deal. For some, it may be most cost-effective to purchase an assembled upper than to build out a stripped upper from scratch.

Just be aware that assembled uppers sometimes do not come with BCGs, muzzle devices, and other necessary parts, and that cost is not a concern for some builders who prioritize customizations.

Check Out Our Collection of Assembled Uppers

MCS Gearup carries a wide range of assembled uppers, as well as AR-15 build kits and hardware kits. We carry effectively everything you need to complete a rifle build at home.

Before you complete your build, make sure to check out our collection of AR-15 barrels, bolt carriers, upper and lower parts kits, and buffer tube kits, all of which you can use to make customizations.

Take a look at our collection and if you have questions about our parts or kits, get in touch with us at or at 239-848-6757.