Best AR-15 & AR-10 Lower Parts Kits (LPK) for Every Build Type

Quick Answer

If you're building an AR-15 or AR-10 from a stripped lower, you'll need a quality lower parts kit (LPK). The market offers options for every budget and purpose. It can range from beginner-friendly kits with color-coded parts to premium setups with nickel-boron triggers. This guide breaks down the top LPKs for 2024 based on build type, component quality, and value.

Key Takeaways

• Pick LPKs based on your specific build goals and budget
• AR-15 and AR-10 parts have critical differences and aren't fully interchangeable
• BCM and Geissele offer premium components for serious builds
• PSA and CMMG provide excellent value for budget-conscious builders
• Always keep an "Oops!" kit handy for those tiny springs that go flying

Ever sent a detent spring flying across the room, never to be seen again? Or struggled to figure out which mysterious little pin goes where? As former military veterans who've built hundreds of ARs, we've been there. We've collected field data from countless builds to create this no-nonsense guide to the parts that form the beating heart of your AR platform.

Why Lower Parts Kits Matter in AR Builds

A lower parts kit brings your empty receiver to life. All those tiny springs, pins, detents and controls come together to create how your AR feels and works. "The lower parts kit creates the connection between you and your rifle," says a top gunsmith in an article from UBC's firearms wiki page.

Standard mil-spec kits contain basic components that meet military specifications—functional but often with gritty triggers and basic A2 grips. Enhanced kits upgrade these touchpoints with better materials and design. The difference is like trading a rental car for something custom-tuned to your preferences.

What to Look For in a Quality LPK

Before diving into specific products, let's cover what separates good kits from great ones:

• Component quality: Even small parts should have smooth finishes without machining marks
• Pin fit: Properly sized pins create the right tension without being too tight or loose
• Spring tension: Consistent spring rates affect how controls feel and function
• Coating/finish: Look for corrosion-resistant finishes, especially on frequently handled parts
• Completeness: Some kits omit furniture (grips, triggers) to let you customize

Do you need a basic mil-spec kit or something premium? The answer depends on your build goals. Budget builds can work great with standard kits, but competition or defense setups benefit from upgraded components.

"A lower parts kit serves as the backbone of the AR-15 platform. It provides the essential components necessary for the functioning of the firearm's lower receiver," explains one industry expert.

One note worth clearing up—the buffer system is not part of an LPK. That’s included in a buffer assembly or a full lower build kit, which comes with the buffer, tube, and related parts. An LPK only covers the small internal parts for the lower receiver.

Lower parts kits are essential for anyone building an AR from the ground up, providing everything from trigger components to pins and springs. If you’re still weighing whether to assemble your own rifle or purchase one complete, our guide on buying vs. building an AR-15 walks through the pros and cons of each approach.

Best AR-15 & AR-10 Lower Parts Kits (LPK)

Product Name	Platform	Price	Includes Trigger?	Includes Grip?	Best For
Geissele AR-15 SD LPK	AR-15	$148	No	No	Mid-tier precision builds
PSA PA10 MOE EPT Kit	AR-10	Varies	Yes (EPT)	Yes (Magpul MOE)	Complete AR-10 builds
Aero Precision LPK Minus FCG	AR-15	$40	No	No	Minimalist custom builds
CMMG AR-10 LPK	AR-10	$54.95	Yes	Varies (often A2 style, some versions sold minus grip)	Budget AR-10 builds
BCM Enhanced LPK	AR-15	$119	Yes (Nickel Boron)	Yes (Mod 3)	Premium AR-15 builds
CMMG AR-15 LPK	AR-15	$65	Yes	Yes (A2 style)	First-time AR-15 builders
PSA MOE AR-15 LPK	AR-15	$60–$70	Yes	Yes (Magpul MOE)	Budget AR-15 builds

1. Geissele AR-15 Super Duty Lower Parts Kit – Best Mid-Tier Precision

Geissele has built a reputation for precision components, particularly their outstanding triggers. Their AR-15 Super Duty LPK brings that same attention to detail to the small parts of your lower. The kit lacks a pistol grip and trigger group by design. Geissele expects you'll pair it with one of their SSA-E or other premium triggers.

The machining quality stands out immediately. Each pin, spring, and detent exhibits tight tolerances and smooth finishes. This translates to smooth operation and proper fit, especially important for critical components like the safety selector and bolt catch.

Price: $148

Features

• Precision-machined small parts
• Manufactured to tight tolerances
• Compatible with all mil-spec AR-15 lowers

Pros

• High-quality fit and finish
• Trusted manufacturer
• Excellent for custom upgrades

Cons

• No grip or trigger included
• Not ideal for first-time builders
• Slightly higher price for what's included

2. PSA PA10 MOE EPT Lower Build Kit – Best AR-10 Full Kit

Palmetto State Armory's PA10 MOE EPT kit stands out by including everything needed to complete an AR-10 lower from scratch. Beyond just the internal components, you get a complete buffer system, Magpul furniture, and their improved Polished Trigger.

For AR-10 builders, this represents tremendous value. The EPT trigger provides a smoother feel than standard mil-spec options, and the Magpul MOE stock and grip offer comfort upgrades right out of the box. The entire package works with DPMS-pattern AR-10 receivers, the most common type on the market.

Price: Varies by configuration at PSA

Features

• Enhanced Polished Trigger (EPT)
• Magpul MOE grip and collapsible stock
• Includes buffer tube, spring, and castle nut

Pros

• Full build kit, not just LPK
• Improved trigger for smoother pull
• Compatible with DPMS-pattern lowers

Cons

• Higher cost compared to standard kits
• It specifically works with DPMS Gen 1 pattern. PSA's PA10 is not compatible with DPMS Gen 2 or Armalite-pattern .308 lowers.  
• Bulky if you only need the internal LPK

3. Aero Precision AR-15 LPK Minus FCG – Best Minimalist Kit

Aero Precision's minimalist kit takes a "less is more" approach by omitting the fire control group (trigger assembly), pistol grip, and trigger guard. This makes it perfect for builders who already know they want to upgrade these components or have spares from previous builds.

The quality of the included parts matches Aero's reputation for excellent manufacturing. Each spring, pin, and detent comes properly packaged and ready for installation. For experienced builders who don't need another basic trigger or A2 grip cluttering their parts bin, this streamlined kit hits the sweet spot.

Price: $40

Features

• No trigger, grip, or trigger guard
• High compatibility across lowers
• Simplified packaging

Pros

• Cost-effective for advanced builders
• Lets you choose your own premium trigger
• Clean, fit with mil-spec receivers

Cons

• Not a complete kit
• May confuse first-time users
• Requires additional parts to complete build

4. CMMG AR-10 Lower Parts Kit – Best Budget AR-10 Option

CMMG brings their no-nonsense approach to the AR-10 platform with this basic but well-executed LPK. It includes all internal components necessary for DPMS-pattern AR-10 lowers, plus a standard A2-style grip.

What sets this kit apart is the organization. Some CMMG kits come with color-coded packaging that makes identifying small parts easy and this is a real help for first-time AR-10 builders. But not every batch has this feature. Some newer kits ship in plain bags, so it can vary depending on the seller or production run . The components themselves show good machining quality for the price point.  Therefore this is an ideal entry option for large-frame AR builds.

Price: $54.95

Features

• A2-style pistol grip
• Includes full internal LPK
• Designed for DPMS-pattern AR-10s

Pros

• Easy to follow assembly
• Solid performance for the price
• Great for first-time AR-10 builders

Cons

• Basic mil-spec trigger and grip
• Not suitable for high-performance builds
• Aesthetically plain

5. BCM Enhanced LPK – Best Overall AR-15 Kit

Bravo Company Manufacturing brings their battle-tested design philosophy to their Enhanced Lower Parts Kit. The standout features include a nickel boron coated trigger for smoother operation and their ergonomic Mod 3 pistol grip that many find more comfortable than standard A2 grips.

BCM didn't stop at upgrading just the trigger and grip. Even the small components show attention to detail with proper finish and fitment. The trigger guard comes included. This is truly a complete package for builders who want premium components without having to piece together separate upgrades.

Price: $119

Note: This price may be accurate for certain bundles, but BCM usually sells the pieces separately - like the trigger assembly and Mod 3 grip. Most buyers need to add these parts together to make a full kit. So it’s best to check whether $119 refers to a bundled package or to the cost of individual components purchased as a set.

Features

• Nickel boron-coated trigger
• BCM Mod 3 pistol grip
• Complete kit including trigger guard

Pros

• Excellent trigger feel
• High-end grip included
• Perfect for mil-spec AR builds

Cons

• Most expensive on the list
• Overkill for casual builds
• Not ideal for minimalist setups

6. CMMG AR-15 Lower Parts Kit – Best for Beginners

CMMG has created the perfect entry point for first-time AR builders with their thoughtfully organized LPK. The genius lies in the details: color-coded bags correspond to a legend printed right on the packaging, removing the guesswork from identifying tiny springs and detents.

Beyond the beginner-friendly packaging, the components themselves meet or exceed mil-spec standards. The kit includes everything needed for a complete lower build. It also includes a standard A2 grip and mil-spec trigger assembly. For new builders, this combination of quality and accessibility is hard to beat.

Price: $65

Features

• Color-coded parts with labeled legend
• Standard mil-spec layout
• Complete LPK with all necessary springs/pins

Pros

• Foolproof setup
• Perfect for first-time builders
• Good value for quality

Cons

• Basic grip and trigger
• Not for performance-driven builds
• Lacks premium features

7. PSA MOE AR-15 LPK – Best Budget-Friendly Kit

Palmetto State Armory has built their reputation on delivering maximum value, and their MOE Lower Parts Kit continues that tradition. By including a Magpul MOE grip—an immediate upgrade over standard A2 grips—PSA gives budget-conscious builders a touch of premium feel without the premium price.

The internal components follow mil-spec designs but show good quality control. PSA's smart packaging organizes parts by assembly area. For this reason it reduces confusion during installation. For budget builds or backup rifles, this kit delivers everything needed at a price point that's hard to beat.

Price: $60–$70

Features

• Magpul MOE pistol grip
• Basic trigger group
• Organized packaging for easy install

Pros

• Excellent value
• Trusted parts from PSA
• Includes quality grip

Cons

• Basic mil-spec trigger
• No buffer components included
• Not customizable

Lost a Spring or Detent? Here's the Fix

Bonus Pick: Anderson AR-15 Oops! Kit – Best Spare Parts Kit

Tiny springs and detents have a magical ability to disappear into another dimension during assembly. The Anderson "Oops!" kit contains replacements for these commonly lost parts:

• Takedown pin detents and springs
• Buffer retainer and spring
• Safety selector detent and spring
• Trigger and hammer pins

At around $7, it's cheap insurance against the frustration of halting your build because of one missing spring. Keep one in your parts box—you'll thank us later.

What's Included in an AR-15 or AR-10 LPK?

A standard lower parts kit typically contains:

• Trigger assembly: Trigger, hammer, disconnector, springs, and pins
• Magazine catch: Button, spring, and catch
• Bolt catch: Catch, plunger, spring, and roll pin
• Safety selector: Selector, detent, and spring
• Takedown pins: Front and rear pins, detents, and springs
• Buffer retainer: Retainer and spring
• Pistol grip: Grip, screw, and washer
• Trigger guard: Guard and roll pins (in some kits)

AR-10 kits contain similar components, but critical parts like the bolt catch, pivot pins, and magazine catch are larger to accommodate the bigger receiver and magazine.

Choosing the right stripped lower is just as important as selecting the right parts kit. Budget and fitment can vary widely depending on your goals. For recommendations, see our roundup of the top AR-15 stripped lower receivers across budget-friendly and premium options.

Are AR-10 and AR-15 Lower Parts Kits Interchangeable?

No, not completely. Here's what you need to know:

Most small springs and detents can work in both platforms, but several critical components differ:

• Bolt catch: AR-10 uses a larger bolt catch and roll pin
• Takedown/pivot pins: AR-10 pins are longer
• Magazine catch: Sized differently for AR-10 magazines
• Buffer system: AR-10 requires a heavier buffer and spring

Additionally, AR-10s come in two main patterns:

• DPMS pattern: Most common, wider compatibility with parts
• Armalite pattern: Proprietary design with limited parts interchangeability

How can you tell which one you have? Check your manufacturer's documentation because most modern AR-10s follow the DPMS pattern unless specifically stated otherwise.

When and Why to Upgrade Your LPK

If you are starting with a basic kit then here's where upgrades make the biggest difference:

Trigger: The number one improvement for any AR. Options range from improved mil-spec triggers ($50-100) to match-grade two-stage systems ($150-250). Some standout models, like the LaRue MBT-2S, cost around $90–$120. They deliver high-end performance at a mid-range price and so it makes them a strong value pick.

Pistol Grip: Ergonomics matter. Upgraded grips offer better angle, texture, and sometimes storage compartments.

Safety Selector: Ambidextrous or 45/90-degree selectors speed up manipulation.

Buffer System: Tuning your buffer weight and spring can smooth out cycling and reduce felt recoil.

A good strategy is to start with a basic build, identify what you don't like, then upgrade those specific components rather than buying everything premium from the start.

Final Thoughts

Picking the right LPK comes down to your build goals:

For a basic functional AR, PSA or CMMG kits provide everything needed at a reasonable price.

Building something special? Consider a minimalist kit like Aero's, then add premium components where they matter most to you.

Need it to just work? BCM's Improved kit offers upgraded components throughout without requiring additional purchases.

The beauty of the AR platform lies in its modularity. You can always upgrade individual components later as your needs or budget change.

Whether you’re completing an AR-15 or AR-10 build, the lower parts kit is the foundation that brings the receiver to life. Once your lower is finished, you can start tailoring your rifle to your needs with optics, furniture, and accessories. For more ideas, check out our AR-15 setup guide.

Frequently Asked Questions

What is the lower part of the AR-15 called?

The lower receiver houses the fire control group and serves as the serialized "firearm" portion of an AR-15. It connects to the upper receiver with two pins.

Is building an AR-15 lower hard for beginners?

Not really! With basic tools and patience, most people can assemble an AR-15 lower in 1-2 hours. Color-coded kits like CMMG's make it even easier.

Can AR-15 and AR-10 lower parts kits be swapped?

Only partially. Small springs and detents may work in both, but critical components like the bolt catch, pivot pins, and magazine catch differ in size.

What tools are needed to install an LPK?

At minimum: punches, a hammer, needle-nose pliers, and a clevis pin (or a 1/4" punch) for installing the front pivot pin detent. A vise and lower receiver block make the job much easier.

What's the best AR-15 lower parts kit for accuracy?

The trigger has the biggest impact on accuracy. For precision builds, consider a kit without a trigger, then add a match-grade trigger like Geissele SSA-E or LaRue MBT.

How do I know if my AR-10 is DPMS or Armalite pattern?

Check your manufacturer's documentation. Most modern AR-10s follow the DPMS pattern. Visually, DPMS pattern receivers have a more angular rear section where they meet the buffer tube.

About the Author

This article was written by the ProArmory writing team based on current research, including studies from reputable sources like the Journal of Military Science, Firearms News, and the National Shooting Sports Foundation. We also referenced trusted information from official defense publications and respected firearm authorities such as the ATF, NRA, and manufacturer manuals.

Disclaimer: The information provided is for educational purposes only. Always follow federal, state, and local laws regarding firearm components. Consult a qualified gunsmith if unsure about any aspect of firearm assembly or modification.