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The Best AR-15 Lower Parts Kits in 2021

Michael Crites

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Disclosure: Products are selected by our editors. We may earn a commission on purchases from a link. How we select gear.

The Russians have a saying – “a man is not a man until he has broken a horse, fathered a child, and built a house.” I’d add “and built an AR-15” to that list. It’s a bit of a right of passage for every firearm enthusiast — one day you’ll decide it’s time to build an AR.

You’ll spend hours pouring over reviews, diving into the forums and /r/guns, agonized over the nuances of BCM vs LWRC vs Aero, and nail the ideal upper. Be it class 5.56, .300BLK, or something more exotic – then you’ll pair it with the perfect custom, stripped lower. 

Of course, that new Bravo Company lower isn’t much more than an expensive door stop without all the bits that help it come to life.

For new builders, sorting through the various kit options, colors, triggers, & variety of furniture can be daunting. Rest assured – with just a little guidance you’ll be off to the range enjoying your new hand-built AR in no time.

In This Article:

Comparison of the Best Lower Parts Kits

Below is my list of the best AR lower parts kits for 2021. I list the best choices in terms of value, performance, design, and cost.

Click on the name to head to the product page, read reviews and check prices or skip ahead to the list of LPKs.

The Best Lower Parts Kits Reviewed

1. Best Overall Kit: PSA MOE Build Kit

This PSA lower parts kit, like most of their PSA-branded products, delivers solid value for money. The PSA MOE EPT Lower Build Kit provides everything you’ll need to complete a stripped lower, which they also sell. 

PSA is a one-stop shop in any AR build as they have a huge number of options for lower parts kits. I liked this kit due to the price point and that it includes a trigger which is much nicer than mil-spec option.

They take the standard single-stage government-style fire control group, then polish the contact surfaces and coat the hammer and trigger in a nickel finish, reducing friction & drag.

The result is a trigger that is smoother than any out-of the-box mil-spec, and makes this LPK a fantastic value.

What We Liked

  • Includes standard combat-style fire control group
  • Upgraded single-stage, target style, trigger  
  • Simple black color-coded scheme
  • Easy to install
  • Quality Magpul components

What We Didn't Like

  • Potential for QC issues
  • Not as tight-fitting as other options

2. Runner-up: CMMG

The CMMG kits are commonly seen in AR builds, and it’s easy to understand why: quality parts in one easy-to-install set.

Plus the CMMG kits has nice touches like oversized takedown detents and color-coded bags to help make the build process easier.

What We Liked

  • Made in the USA
  • Takedown pin detents are oversized for easier installation
  • Trigger doesn’t much creep for mil-spec
  •  Color coded bags simplify installation
  • Includes extra springs

What We Didn't Like

  • Some find the grip to be blocky
  • Buttstock not included

3. Best Trigger Upgrade LPK: Geissele

Geissele has built its reputation on slick-running ARs, so it makes sense that they’d be in the LPK market as well.

The Geissele AR15 Lower Parts Kit is the kit you’ll want if you want to build your AR around a top-tier trigger and also need the other components of the fire control group, a trigger guard, and other furniture.

What We Liked

  • Comes with the major AR lower components
  • Crisp, easy-to-use safeties.
  • Fits a wide variety of mil-spec lowers
  • High-quality finish

What We Didn't Like

  • Since they make great triggers, I’d like to see a kit with the fire control group included
  • The magazine release button may need hand fitting

4. Best Flat Trigger LPK: PSA Sing Stage

 This kit by PSA has one of the nicest triggers available in any LPK, and I’d recommend it to anyone who’s selective about trigger feel or prefers a flat-faced trigger. I have one of these single-stage flat-faced triggers on my PCC and it’s as snappy as a mouse trap.

The ambidextrous safety is a great touch, especially for left-handed shooters.

AR Lowers - PSA PCC Lower Alt
My PCC lower was built around a PSA single-stage, flat-faced trigger. Different strokes, as they say.

What We Liked

  • Comes with an excellent single-stage trigger.
  • Has a buffer retainer, which not all kits do.
  • Safety is ambidextrous and has an auto setting.
  • Included a hex key, they know you can’t find yours either.

What We Didn't Like

  • With an auto safety, perhaps a hardened hammer would have been nice.

5. Best Minimalist Kit: PSA MFT

If you have a stripped lower and need all the bits and pieces to complete a minimalist rifle, this is the way to go. With the PSA MTM Minimalist EPT Lower Build kit, you’ll have built a mil-spec lower with the Mission First Tactical (MFT) minimalist furniture set, which is a go-to setup for many personal ARs. 

If you want a no -frills, minimalist rifle this kit is worth every penny.

What We Liked

  • Comes with a lightweight buttstock
  • V2 style pistol grip 
  • Includes buffer tube
  • Complete kit – nothing additional needed
  • Available in multiple color options

What We Didn't Like

  • Could include a better trigger

What’s a lower parts kit?

Often the finishing flourish of a build, a lower parts kit contains all the components you need to complete the lower receiver of your AR-15.

Without the kit, your gun simply won’t function.

Every AR starts its life as a bare piece of metal (or polymer if that’s your jam), and transforming that piece of metal into a proper rifle or pistol requires a trigger, bolt catch, safety selector, and set of springs.

You’ll find at least this much in any lower parts kit. You can also include the lower furniture (grip & buttstock) to round out a complete build kit.

Bushmaster AR lower diagram
This classic Bushmaster lower breakdown gives you a sense of the components involved in both the complete lower and the LPK. While this is a rifle lower, carbine lowers are similar but with shorter buffers, springs, & buffer tubes.

What to Look for in a Quality Lower Parts Kit

AR Lowers - Daniel Defense Lower
This lower uses a mil-spec trigger, but your kit should fulfill the goals of your build.

While it depends totally on you — but in general it’s not a bad idea for a first-time builder to ask for a little help from someone with experience stitching a lower together. 

1. Fit with your build

AR Lowers - Group
Lots o' lowers. Without an LPK these are just expensive paper weights.

You’ll need everything your lower doesn’t have. For folks interested in updating or upgrading bits and pieces, you’ll need new springs and a bolt catch – that’s a basic lower parts kit. 

For others who are completing a stripped lower, you’ll need a complete lower parts kit with all of the above plus a trigger, trigger guard, grip, buffer tube assembly & stock.

2. Trigger Assembly

AR Lowers - Group
Lots o' lowers. Without an LPK these are just expensive paper weights.

The lower parts kit influences handling & trigger feel, so it pays to choose carefully.

Some kits come with a mil-spec trigger, which works, is relatively inexpensive, and many shooters are comfortable with – but mil-spec may not be your goal. In that case, look for a kit that offers a single-stage trigger for a cleaner break. Some kits will offer various color options on the furniture, so you can impress your shooting buddies with a buttstock that matches your kicks.

You can pick up budget options, but whatever you save in cash will almost certainly be paid out in frustration when you blow a spring or hate the trigger.

3. Completeness

Also, consider what the kit includes. Make sure it includes everything you need to complete your rifle. If you’re missing the fire control group and don’t pick up the right kit, you’ll be right back here looking for parts instead of heading to the range.

In the market for a complete lower? Check out my list of some of the best AR-15 lowers available today.

Types of Lower Parts Kits

Lower parts kits aren’t particularly complicated, but a little attention to detail goes a long way. The first step is to determine the kinds of components you’ll need for your build. A well-equipped kit will have everything you need but may be overkill if all you want is an updated fire control group (FCG). Once you are clear on the components you need, you can create a shortlist of the specific kits that will get you home.

There is no perfect lower parts kit because everyone has different priorities and sacrifices are part of the process. Only you can decide what’s most important. Are you doing a refresh your everyday shooter’s lower? Do you need a grip and spring set? Are you looking for more of a build kit that gets you all the furniture and trimmings? There are lower parts kits designed for a range of needs, so spend some time familiarizing yourself with the landscape of kits before you pull the trigger.

Fire Control Group (FCG) Only

The least commitment when planning a low rebuild, the FCG houses the trigger, its integration with the safety, and the release of the hammer or striker. These components — the hammer or striker, trigger, disconnector, springs, pins, and sear — are all contained in a single kit allowing you to upgrade just those components and reassemble the rest of the gun unchanged, leaving you with a smoother, improved trigger feel without the level of investment required with larger, more complicated kits. 

Lower Parts Kits

If you want to update the FCG, grip, trigger guard, and internal Springs and pins, you’re looking for a true lower parts kit. These will generally include 7 springs, the safety selector, takedown pins, mag release, all the FCG components, and a grip. You’ll often see these kits packaged with a variety of upgrade options, like single-stage or 2-stage triggers from premium brands like Geissele or CMMG. These are also often available without the FCG, so if you like your trigger and only want to update other components or only need the springs and pins, an LPK sans FCG is the way to go.

Lower Build Kits

Lastly, lower build kits include the components to both upgrade lower receiver internals and update external furniture, such as stocks, buffer tubes & springs, and a castle nut, latch plate, & detents. If building a new AR from a stripped lower, these kits include everything you need to finalize the build from a mil-spec stripped lower, so they’re the most straightforward way to complete a lower build with a single purchase. 

Lower Parts Kit Pricing

  • Less than $50: For less than $50, your options are largely limited to fire control groups and budget-oriented lower parts kits sans FCG. 
  • $50-$150: Lower parts kits aren’t particularly expensive and are generally between $50 and $100 for a complete LPK inclusive of fire control group. This may not include premium triggers and almost certainly won’t include furniture, but if you’re budgeting out an AR build, $100 or so is a good range to anticipate paying for a full lower parts kit.
  • Over $150.  When you’re putting a couple of benjamins together you’re in the build kit range, which will get you everything you need to complete a lower build and some snazzy new furniture. You can also find nice trigger upgrades in complete LPKs (sans furniture) at this price point. 

Why buy an LPK?

Take a trip to any aspiring armorer’s house, and we’re willing to bet there’s a box of AR springs here, pins there, and a tool station somewhere.

Building (or rebuilding) your lower with an LPK allows you to improve its function or keep your rifle operating just the way you like it. You can exercise control over the component quality, trigger feel and consistency, and look and feel of your rifle so you can fine-tune your shooting precision, build that badass AR pistol just like you want, or keep ol’ glory rolling for a few thousand more rounds.

A quality AR isn’t cheap, but keeping your receivers in tip-top shape is surprisingly economical. 

How we picked these products

When reviewing guns or gear, we get our hands on as many products as possible, but there are times when certain products or categories are a real challenge — be it availability, cost, or simply a lack of resources — we can get stymied going hands-on with all the potential candidates. Plus, the LPK category is massive, so rather than present a never-ending list of all the parts kits on the planet we selected those which we felt best represent the price points laid out above — giving you a solid representational list to serve as a jumping-off point for your own research (you are going to do you own research, right?)

To avoid disappointment or steering you in the wrong direction, we bolster our own experience with conversations with experts, comb through reviews on retailer sites & sales data, review industry publications, other blogs, and otherwise surface the best information available.

We aim for all thriller, no filler, as they say.

Conclusion

Here, I’ve run down some of the best AR-15 lower parts kits on the market. While they vary in features and completeness, there’s almost certainly a kit out there that will have the parts you need.

I like the PSA MOE kit for most builds, which gives you some additional flexibility by including all the components you need to fully complete a lower receiver while letting you pick your furniture to finish out your build in the way you want. 

That said, some of the other offerings are certainly compelling if you’re looking for specific features such as a fully complete build kit or trigger upgrade, both of which I have provided recommendations above, so I encourage you to check out all your options. Happy hunting!

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