The AR platform is the most popular sporting rifle bought and sold today. It’s also the most built firearm in circulation. That’s because the venerable ArmaLite Rifle is easy to fabricate – and hundreds of manufacturers are happy to provide broad catalogs of high-performance, custom components for just this purpose.
But picking the right AR15 parts for your custom build means the difference between investing good money in a reliable, accuracy rifle and one that’s inaccurate, heavy, and wasteful on the wallet. So let’s go over the optimal component selection for piecing together your own custom black rifle for a successful day at the range or in the hunting blind.
Building a Custom AR-15: Required Parts
Regardless of the caliber and configuration you want to build, you’ll need the following components. Many are standardized – they’re interchangeable, regardless of caliber or configuration – but we’ll go over compatibility next.
Required parts include:
The Upper Assembly
- Barrel w/ Barrel Extension
- Handguard w/ Barrel Nut
- Gas Tube & Gas Block
- Stripped Upper Receiver
- Bolt Carrier Group
- Charging Handle
The Lower Assembly
- Stripped Lower Receiver
- Lower Parts Kit
- Buffer Tube
- Recoil Spring
- Weighted Buffer
- Stock (Required for rifle) or Brace (optional for pistols only)
To make custom builds easier, many parts makers preassemble these components. You can buy two halves of your custom rifle – the upper assembly, and lower assembly – with all the above components installed in either one. Then it’s a simple matter of mixing and matching the upper and lower of your choice to achieve the desired caliber and configuration.
The Optimal AR-15 Parts for Any Build
Best Barrel Lengths& Twist Rates by Caliber
For starters, any rifle needs a barrel measuring at least 16” in length. That’s the minimum legal length, according to the ATF (any rifle equipped with a shorter barrel is considered a short-barreled rifle and needs special paperwork to legally own).
Twist rate describes how quickly the rifling in the barrel rotates, and it determines the stability of the round while it’s in flight.These are the optimal barrel lengths and twist rates for the most AR’s most popular calibers:
- 5/56.223: 16”, 1:7 or 1:8 twist rate.
- 300 BLK: 16”, 1:7 or 1:8 twist rate.
- 6.5 Grendel: 20”, 1:8 twist rate.
- 9mm: 16”, 1:10 twist rate.
- .308 Win: 20”, 1:10 or 1:12 twist rate.
Get a Free-Float, M-LOK Handguard
These handguards help improve accuracy because they don’t attach directly to the barrel. They’re also lighter than other options (like quad rails) and they’re generally more comfortable to hold. The M-LOK rail system has become the most popular attachment method for securing additional AR parts to your handguard, including lights, lasers, and foregrips.
Use a Low-Profile Gas Block
These gas blocks hide underneath the handguard, eliminating the bulky and heavy blocks that incorporate the front sight post. They’re also available as adjustable systems, allowing you to fine-tune the gas traveling back to the bolt. This allows you to reduce the pressure and felt recoil, and it helps prolong the life of your receivers and their internals.
Read Also: What You Should Know About Water Heaters
Get a Mid-Length Gas System (Unless It’s 300 Blackout)
Many off-the-shelf AR-15s come with carbine-length gas systems. The length of the system determines how much gas pressure returns to the bolt carrier group. Carbine setups are over-gassed, meaning they provide too much energy and felt recoil.
Mid-length gas systems provide reliable functionality without the over-gassing issue. This reduces felt recoil without the need to vent extra gas with an adjustable gas block. The only circumstance in which a short gas system is required is when you’re chambering 300 Blackout. This round is capable of functioning as a low-energy subsonic load, which dictates the need to use the shortest gas system possible (pistol-length).
Get a More Comfortable Rear Grip
The standard AR-type pistol grip is angled in such a way that it causes unnecessary strain on the wrist and, by extension, makes recoil control and good trigger squeeze more difficult to manage. A grip with a more vertical profile, like the Magpul MOE K2 provides a more natural hand grip and reduces this strain.
Ditch the M4 buttstock for One with Rubber
Just like that factory-style grip, the AR’s “mil spec” buttstock just isn’t comfortable. It fails to provide an adequate cheek weld (that’s the placement of your cheek against the stock to obtain a sight picture through your iron sights or optics) and it provides no recoil reduction because it has no padding.
Magpul once again saves the day with a lightweight and more ergonomic option that generally provides a better cheek weld. Plus, their stocks come with rubber pads that help insulate against the recoil energy passing into your shoulder.
Buy a Latch Plate with a Sling Mount
The latch plate is the component that helps lock the buffer tube into the lower receiver. This deceptively simple component is often overlooked as an opportunity to upgrade your AR. This is the perfect place, relative to center of gravity, to mount a single-point sling.
This makes carrying your rifle much easier, and with the sling placed in this location, your rifle naturally rests in a comfortable, near-vertical placement along your chest.
Upgraded latch plates often come with loops for attaching a clipped sling, or a circular hole that interfaces with locking QD sling studs. Either option is preferable to the factory plate, which provides no sling attachment at all.