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What’s the Best AR-15 Lower Receiver Parts Kit? Includes Buying Guide

best ar 15 lower parts kit

Building an AR-15 allows you to completely customize every part of your gun to exactly fit what you want from your rifle. However, choosing the lower parts kit is also one of your most complicated parts of your build, as it may affect your finished product’s quality and reliability. To help you find the best AR-15 lower parts kit, our team of experts tested out ten lower kits for you to choose from. 

To know more about the features of these highly customizable kits, keep on reading.

OUR #1 RATED

CMMG – AR-15 LOWER PARTS KIT

OUR #2 RATED

AERO PRECISION – AR-15 LOWER PARTS KIT

AERO PRECISION - AR-15 LOWER PARTS KIT

OUR #3 RATED

CMC TRIGGERS – AR-15 LOWER PARTS KIT

1. CMMG - AR-15 Lower Parts Kit

The CMMG – AR-15 kit is an AR-15 lower parts kit that contains every internal part needed to complete or rebuild an AR lower receiver. It features high-quality components designed to work with each other to ensure smooth operation and everything a shooter needs to complete a lower receiver build.

These components come in color-coded bags organized in related parts for easy assembly, excellent for beginners who had never built an AR-15 before. The CMMG also includes molded-polymer A2 pistol grips and a Mil-Spec trigger that offers a single-stage 6 to 6½ lbs service rifle pull.

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2. Aero Precision - AR-15 Lower Parts Kit

The Aero Precision Enhanced Lower Parts Kit is a lower receivers kit with a Magpul MOE grip and billet trigger guard. Its components are manufactured in the United States of America and weigh 8.1 ounces altogether.

This Enhanced Lower Parts Kit comes with 28 different mil-spec components perfectly tailored to fit your AR. Each of the components of this Enhanced Lower Parts comes with corrosion-resistant coatings, giving you durability and smooth operation.

AERO PRECISION - AR-15 LOWER PARTS KIT

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3. CMC Triggers - AR-15 Lower Parts Kit

The Sharps Bros. unit is a budget AR rifle complete upper receiver that uses Mil-Spec Type III hard coat anodize billet with dust cover. This upper comes with a forward assist kit installed, a charging handle, and a bolt carrier group.

It is also constructed from 7075-T6 aluminum and features a “SHARPS BROS” discretely engraved on both sides. This complete upper receiver only weighs 9 oz and best used for .223, 5.56 NATO, .300blk, and 6.5 Grendel builds.

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4. KE Arms LLC - AR-15 GI Lower Parts Kit

The KE Arms AR-15 GI Lower Parts Kit comes with an enhanced polymer winter trigger guard, secured with roll pin and set screw roll pin and set screw for easy installation. It also features an A2 pistol grip constructed of molded glass-filled nylon for durability and optimal strength. It also boasts a fire control group that features a trigger and safety selector with black oxide coated hammer spring, magnesium phosphate coated hammer, and trigger spring, spring bolt catch, and disconnector spring for long service life.

KE ARMS LLC - AR-15 GI LOWER PARTS KIT

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5. Brownells - AR-15 Lower Parts Kit 5.56

The BROWNELLS KIT 5.56 is an AR-15 lower receiver best for building or rebuilding an AR-15 rifle. This 5.56 lower parts kit comprises all high-end, Magpul MOE hardware and Mil-spec parts, packed in colored bags for easy installation. This kit is ideal for upgrading some of the more common parts right. 

This kit includes takedown pin, receiver pivot pin, takedown pin detent, bolt catch, bolt catch plunger, buffer retainer, magazine catch, trigger guard assembly, and safety selector. This kit comes with a buffer tube assembly with a carbine buffer, too. However, this kit doesn’t contain a fire control group or pistol grip

BROWNELLS - AR-15 LOWER PARTS KIT 5.56

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6. Geissele Automatics LLC - AR-15 Lower Parts Kit

The Geissele Automatics LLC Kit contains top-quality steel for all the components necessary and high-end internal parts to get your lower part operational. This kit doesn’t come with the trigger and pistol grip that you may not want. 

This kit also features lower receivers manufactured to “mil-spec” M16 / M4 dimensions ensuring optimum fit and function in your AR rifle or carbine. This kit also comes with a fire control system comprising hammer, trigger, disconnector, and pins, all “personal” parts of any custom AR-15.

GEISSELE AUTOMATICS LLC - AR-15 LOWER PARTS KIT

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7. M&P AR-15 Complete Lower Parts Kit

The M&P AR-15 Rifle Complete Lower Parts Kit is an Enhanced Lower Parts Kit that includes everything you need to complete your lower receiver. All you have to do is find a stripped lower receiver and stock assembly of your choice. This kit is easy to install and also gives you the flexibility to add your own aftermarket upgrades. 

The M&P AR-15 Rifle Complete Lower Parts Kit also features 20 total components built on par with military specifications. However, it doesn’t come with a lower receiver.

M & P - M&P AR-15 COMPLETE LOWER PARTS KIT

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8. Double Star - AR-15 Lower Parts Kit

The DOUBLE STAR LOWER PARTS KIT is an AR-15 lower receivers kit that features high-quality American made parts and everything you need to complete your lower receiver. The kit includes a fire control group constructed from mil-spec heat treated 8620 steel, made to last for the weapon’s lifetime. It also comes with a smooth finish on all touchpoints and a crisp trigger pull with minimal creep or drag. Its lesser lower kits also use metal injected molded, making this kit an affordable choice. 

Double Star also uses coiled steel spring pins instead of the standard split roll pins, so their parts are easier to install than the others. This kit has everything you need, including an additional takedown detent and spring as a back-up if one spring flies away during installation, never to be seen again.

DOUBLE STAR - AR-15 LOWER PARTS KIT

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9. Critical Capabilities LLC - AR-15 Lower Parts Kit

The Critical Capabilities LLC AR-15 Lower Parts Kit is an AR-15 lower receivers kit that comes in two variants; one has a pistol grip and without a pistol grip. However, both lower parts kits include a trigger, which is better than a standard mil-spec trigger. The included triggers are Enhanced Longitudinal Grind (ELG) ground and polished in line with the direction of the trigger movement. 

It also provides a cleaner break, smoother mil-spec trigger press, and a better platform for doing your trigger job. Furthermore, this kit includes all the necessary lower receiver hardware, machined or forged to ensure durability at all weather conditions. The lower parts feature a thick and matte black hard coat anodized finish.

CRITICAL CAPABILITIES LLC - AR-15 LOWER PARTS KIT

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10. LUTH-AR LLC - AR-15 Lower Parts Kit

The LUTH-AR LLC – AR-15 lower parts kit is also one of the best AR-15 lower receivers kits that contain all the parts necessary to turn a stripped lower into a complete receiver ready for the buffer system, buffer tube, and stock of your choice. This kit packs all its basic mil-spec parts separately for easy assemblies like catch roll pin, pivot pin and safety selector detent.

It also completes mil-spec AR-15 fire control components like the trigger, disconnector, hammer, and all the pins-n-springs. This Luth-AR kit also includes a standard A2-type plastic pistol grip, a fancier, aftermarket grip

LUTH-AR LLC - AR-15 LOWER PARTS KIT

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What’s In A Lower Parts Kit?

  • Pistol Grip
  • Buffer Retainer and Spring
  • Magazine Catch Assembly
  • Safety Selector
  • Safety Selector Detent
  • Safety Selector Detent Spring
  • Trigger
  • Trigger Spring
  • Trigger Pin
  • Trigger Guard Assembly
  • Hammer
  • Hammer Spring
  • Hammer Pin
  • Disconnector
  • Disconnector Spring
  • 2 Takedown Detents and Springs
  • Bolt Catch
  • Bolt Catch Spring
  • Bolt Catch Roll Pin 
  • Bolt Catch Plunger
  • Rear Takedown Pin
  • Pivot Pin

Things to Consider

things to consider

Budget 

When buying the best AR-15 lower parts kits, it is best to remember that the primary reason for buying a build kit or parts you need rather than separately purchasing them is to save money. Try to calculate each part’s actual cost when you buy them individually and compare the cost when you buy the best AR lower receiver kits on the market. 

Ergonomics  

Ergonomics is also one thing that you must consider when buying an Enhanced Lower Parts Kit. It is best to focus on their materials or the quality control of the company. Determine whether the parts are mil-spec or premium build, as it may greatly affect your lower parts kit choice. Mil-spec kits come with simple and easy to build operation, while premium builds are mainly determined by personal preferences and are more expensive.  

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Functionality 

Most shooters are usually enticed with the overall “fit and finish” of the lower parts kit, which is an important consideration when assembling the parts. The fit and finish of your lower parts kit also dictate your build’s functionality after installation. Hence, we recommend that you learn every part you slid into your build to make it function at its best potential.

Durability

It would be best to consider your lower parts’ durability to ensure your build’s overall functionality and life span.

We suggest that you find the best lower parts kit like CMMG that offer precision-machined components made of top-quality steel with advanced finishing techniques, nickel boron, or Teflon.

Nickel-boron coatings were synthesized on mild steel by the electroless deposition method. [1] These types of coatings are corrosion-resistant.

durability

Inclusions 

Not all parts kits or build kits for AR-15 come with everything you need to build your lower parts. So, having many inclusions are helpful for your decision-making. We recommend that you find the best lower parts kit that includes a Fire Control Group, stock and buffer system, pistol grip and trigger that could make your build better. You may also install a free float quad rail for more functionality.  

FAQs

AR-15 lower parts kits aren’t the same. Some kits are mil-spec and premium built, and there are a few instances that the parts’ sizes differ from one another. Some kits provide roll pins for the trigger guards that are oversized for AR rifles. These instances usually happen because of the type of coatings and materials used for each part.

No, the AR-10 and AR-15 lower parts aren’t the same and are not interchangeable. Although most AR-15 LPKs will work with the AR-10, this isn’t the case for AR-10 lower receivers. The AR-10 shoots larger calibers, so its receiver and magazines are larger than AR-15.

Based on reliable reviews, buying quality lower parts kit matters because quality usually equals durability and functionality. Companies tend to price their kits higher when their quality control is higher and better, too.

And Our #1 AR 15 Lower Parts Kit is...

Based on extensive research, the CMMG – AR-15  is our #1 AR-15 lower parts kit because it features high-quality and mil-spec components designed to ensure smooth operation. This kit also comes in color-coded bags to organize related parts and for easier assembly. 

It also includes a molded-polymer A2 pistol grip and trigger with a single-stage 6 to 6½ lbs service rifle pull. This lower parts kit is also best for the first time lower receivers builders.

Our #1 Recommendation

CMMG – AR-15 LOWER PARTS KIT

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