9 Best AR-15 Complete Upper Receivers in 2024 (Don’t Miss Out)

Budget

Another great thing about building your own AR is the flexibility you have with budget. If your budget is limited, or you want the best bang for your buck, the AR platform lets you splurge where it matters most (like your barrel) while saving money in other areas. Knowing the primary purpose for your build will help you determine where to spend and where to save.

Barrel

When I start a build, the most important consideration in the upper assembly is the barrel. Your barrel determines the longevity and durability of your AR-15 but most important, it has the single most impact on how accurate your gun will shoot.

Caliber

Many caliber options are available for the AR-15 platform chambered in rounds of 45mm in length or less including chamberings from .22 long rifle up to 50 Beowulf.

.223 Remington was the original AR-15 cartridge and the M16A1 was originally designed for 5.56×45 NATO. It continues to be the least expensive, accurate semiautomatic platform capable of keeping bullets supersonic out to targets at 600 yards.

Shooting a .223 Remington cartridge in a 5.56mm chamber is safe (but not the other way around) for the sake of versatility but there are tradeoffs in terms of decreased accuracy and velocity. If you need that flexibility for competitions or if you will use your rifle for both home defense and hunting, it may make sense for you to go that route.

The .223 Wylde chamber is used on .223 Rem rifle barrels to allow them to safely fire either .223 Remington or 5.56×45mm NATO ammunition.

Twist Rate

With caliber determined, think about the types of bullets you will shoot which will determine what twist rate your barrel needs to have.  Twist is the distance in inches that it takes for the bullet to make one revolution in the barrel. A 1:7″ twist means that the bullet will make one full revolution in your barrel every 7 inches compared to a slower twist rate of 1:12″ where the bullet will make one full revolution in 12 inches.

This revolution stabilizes the bullet in the air. A twist rate that is too high or low for a particular kind of bullet will cause accuracy to decline.

Barrel Length

Barrel length affects handling – both in how it feels for you as the shooter and how it shoots because the length will affect the bullet velocity.

Longer barrels add more weight and help with more accurate aiming making them a good choice for precision shooting and longer-range hunting. A heavier rifle will produce less recoil, which helps with follow-up shots, but the extra weight can be fatiguing. A shorter barrel is well-suited for self-defense and other closer-range scenarios because it’s lighter and easier to maneuver.

A 16″ barrel maintains very good accuracy but if you need higher velocities, choose a 20″ or longer.

Barrels shorter than 16” should be on an AR pistol lower. Otherwise, it’s considered a short-barrel rifle and subject to NFA rules.

Barrel Diameter

Next you want to make sure to choose the barrel diameter, sometimes referred to as the profile or contour, that best suits your needs. The diameter will determine how long your barrel will maintain accuracy during long strings of fire.

• Thinner “pencil” or A1 barrels are lighter to carry, but will heat up faster.
• Heavy barrels are heavier, but heat up slower.
• Medium-weight or standard barrels offer a decent compromise between weight and heat management.

Manufacturers aren’t consistent with naming conventions, but a rule of thumb is:

• .625″ for A1 or “pencil” barrels
• .750″ for standard barrels
• .936″ for heavy barrels

Chrome Lining

Gas System and Handguard Length

Now that you have made all the important decisions about the barrel, you can determine which gas system length is best for you. A longer gas length equals longer dwell time in the barrel resulting in smoother, softer shooting and less wear on your bolt.

• Rifle length is best on 20″ and longer barrels
• Mid-length is ideal for 14″-18″ barrels
• Carbine-length can be used with 10-18″ barrels. Shooters that want to maintain the classic A2 military style often use these on 16″ or 18″ barrel.
• Pistol-length is designed for use on barrels that are 10″ or shorter

Gas Block and Sights

The next option you will choose is the profile of your gas block which affects the type of sights you use. Two of the most common are:

• Standard front site base – use with A3 or Flattop Receiver; if you are using an optical sighting system, the height of the standard front sight partially obstructs the field of view, making it less than ideal
• Low-profile gas block – ideal for use with optical sights. Can add detachable and flip-up rear sights designed to work with your standard front sight, allowing you to co-witness by using the two in conjunction or switch between iron sights and an optical sight.