When building an AR-style rifle with an AR 15 complete upper, you’ll want to make some important decisions as to what parts to pair with it or choose before you buy the assembly.
And, as will be the case in a complete AR upper, since those parts will come with it, you will have to shop wisely. If you built with a stripped upper, you could make changes along the way. With a complete upper, what you get is what you get, and if you don’t get the right upper, you’ll end up spending more to swap out parts.
So, when considering an assembled upper, here are 5 parts that you will want to weigh carefully.
The Barrel (Length, Alloy, Rate of Twist, Etc.)
Once you’ve settled on a caliber, length of the barrel is probably the next most important thing to take into consideration.
The most common barrel sizes are probably 16” barrels (with which you can create M4-style carbines) and 20” barrels (which are used to create full sized, M16/AR15-style rifles).
There are longer and shorter barrels, too, which can be used for long-range shooting (on the longer end) and for AR pistols (on the other end, as in the case of 5 inch uppers and AR pistol uppers).
The length of the barrel is important because it will impact the handling, the power, and potentially the accuracy of the rifle.
All else being equal, a rifle with a shorter barrel will be lighter and handle much better, especially at short ranges. This makes rifles with shorter barrels often the top choice for defensive applications, and for some competition, such as 3-gun.
As for rifles with longer barrels, a few extra inches can give a big boost to muzzle energy and therefore power, as well as accuracy. Most shooters agree that a longer barrel is better for long-range shooting because it helps boost accuracy, even though that comes at the expense of handling.
Also, when evaluating the barrel of an AR 15 complete upper receiver, consider also the rate of twist and the steel of the barrel, as there are both carbon and stainless barrels, along with a wide range of finishes, like Cerakote and nitride, both of which improve corrosion and wear resistance.
The Muzzle Device
The majority of AR15 barrels are threaded, and many come with muzzle devices pre-installed. Some of these even come with integral muzzle devices.
For the most part, the most common muzzle device you will encounter is a flash hider. These are useful as they help conceal your muzzle flash, which can keep you hidden, and also prevent your muzzle flash from obscuring your target.
While flash hiders are beneficial for some shooters, others consider muzzle brakes or even suppressors superior.
A muzzle brake will basically change how gasses are dispersed at the muzzle, combating both recoil and muzzle flip. In most cases, a good muzzle brake can slash felt recoil by 50% or more without adversely affecting shot power. They also fight muzzle flip, enabling faster, potentially more accurate follow up shots.
Suppressors are also popular, but as these are NFA items, getting one will require you to go through the rigmarole of getting a tax stamp and all that. They do, however, also slash felt recoil and substantially cut muzzle pop and overall volume.
The Handguard
The handguard that comes with the AR 15 complete upper is another component you’ll want to choose carefully.
This is something you can change out after the fact, but the length of the barrel will limit you somewhat, so be aware of that. Also, as is the case with the other parts mentioned here, when you buy a complete upper you’ll be getting a handguard anyway, so to save money you might as well just get the one you want.
There are three common types of handguards on the market right now that are fairly popular. These are Picatinny handguards (commonly in a quad rail upper configuration) along with KeyMod and M-LOK rail systems.
Pic rail systems, which often come with quad rail upper systems, consist of a series of slots and grooves. These are the oldest and arguably the most durable types of rail systems commonly produced. They offer a strong attachment point for accessories, but they are heavy and can be uncomfortable to carry and shoot without gloves.
Both KeyMod and M-LOK rail systems are much newer and lighter than Picatinny rail systems, and some are even made from very lightweight polymers. They also offer strong attachment points, but there are fewer accessories available for them. Also, they are a lot smoother and more comfortable to carry and shoot than Pic rail handguard and quad rail uppers are.
The AR15 Charging Handle
We previously wrote an entire article about when it makes sense to change your AR-15 charging handle. The good news is that not all uppers come with charging handles and there are some affordable options out there.
If the complete AR-15 upper you had your eye on has a cheap charging handle, swap it out for one that offers better ergonomics, ambidextrous use, and helps port gas away from your face during operation.
The Bolt Carrier Group
Last but definitely not least you will have to consider the bolt carrier group, specifically the coating of the bolt carrier group.
Some AR 15 complete uppers do not come with bolt carrier groups, so this one you may need to shop for on your own. One of the most common coatings is a black phosphate coating, AKA a “mil-spec” coating.
These are affordable and relatively low maintenance but they do require a good deal of liquid lubrication to keep everything working smoothly.
There are other modern BCG coatings - like titanium nitride, black nitride, diamond-like carbon (DLC) and nickel boron, all of which offer superior permanent dry lubricity than mil-spec coatings.
These modern coatings require less liquid lubrication than alternatives, making them relatively low maintenance and trapping less fouling and dirt in the action. It also makes them easier to clean than their “toothier” counterparts.
They can be pricey, but investing in a bolt carrier group with an advanced modern coating that offers better permanent dry lubricity can be worth it in the long run.
Getting Started with an AR 15 Complete Upper from MCS Gearup
Getting ready to build an AR-style rifle with an AR 15 complete upper receiver? Start here and check out our full inventory of parts if you want to swap anything out. We sell everything you need to customize a build, from barrels to gas systems to buffer tubes.