Best M16 Lower Parts Kit – Complete Your Build With Ease

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Whether you are building a new M16 or repairing an old rifle, you will definitely need an M16 lower parts kit.

There is a dizzying array of parts kits out there marketed by various companies.

Different parts kits serve different needs, and not all are equal, so follow our guide for the best M16 lower parts kits.

Comparison of the Best M16 Lower Parts Kits

  • Includes a spare takedown detent and detent spring.
  • Spring pins are made of coiled steel that won't creep out.
  • All touch points are finished for the smoothest operation.
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  • Great parts kit for repairs or to keep spare springs around.
  • All parts included meet or surpass military specs for quality.
  • Designed and made in the USA by a family-owned company.
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  • Made with pride right here in the US of A.
  • An excellent backup kit in case of sudden part failure.
  • Contains all the most commonly lost or worn out parts.
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What Comes in the Kit?

A good lower parts kit will contain all the components that go inside or attach to your lower receiver. Some kits will only contain one sub-category of these parts.

Colt - Lower Receiver Parts Kit

A full parts kit will include an M16 sear, sear spring, sear pin, a buffer detent, a buffer detent spring, an A-2 pistol grip, a pistol grip screw, a pistol grip screw washer, a bolt catch assembly, a front pivot pin, a mag catch assembly, a rear takedown pin, two takedown pin springs, two takedown pin detents, an M16 fire control group, and all pins and springs for the fire control group.

Ideally, all of these parts will be made in the U.S.A. Occasionally, you will get parts pits just of high-quality replacement springs or focused around a specific assembly. 

Do You Need Any Missing Parts to Complete Your Build?

All the parts you need to build an M16 lower receiver will be included in a complete parts kit, as listed above. You will, of course, also require a stripped-down lower receiver. Some tools are also necessary to build an M16. Having a quality set of all the tools necessary will help you assemble everything properly and guarantee that you come out with the highest quality product.

First and most importantly, you should have a good clean surface to work on, such as a workbench. A quality vice is also a huge plus. A set of punches for installing the M16's various pins is a must.

The best option is to get brass roll pin punches, as standard punches can damage the M16's many roll pins. A stock wrench is absolutely necessary for the castle nut. A light ball peen hammer and a brass or nylon hammer are also major necessities. Needle-nose pliers and a flat-head screwdriver are very useful, too.

Qualities of Our Favorite Kits

The most important thing for choosing the best firearms components, including lower receiver parts kits, is to find a well-proven, well-reviewed product from a reputable, well-established manufacturer. For example, a company like Brownells, one of the nation's major firearms and firearm component retailers.

They have experience with sales and returns to know what works and what customer feedback has been. They use this knowledge to produce many of their own components, including lower parts kits.

These are often unsurpassed in quality. A good manufacturer will list the materials and manufacturing methods used in producing their lower parts kit. Each individual component has its own specifications. It takes some research and more space than we have here to delineate the ideal details of every lower parts kit component.

Tolerances should be high and materials should be the most appropriate for that component. Besides this, the price, packaging, and shipping condition for every parts kit should be reasonable. Some manufacturers place an excessive level of markup on their parts kits.

There is no reason to pay vastly more than the manufacturing process costs. The packaging is important so that parts don't get damaged or lost in shipping.

Review of the Best M16 Lower Parts Kits

There are a lot of options out there, but not all come with great quality or at a reasonable price. Follow our guide for the best M16 lower parts kits.

1. Doublestar Lower Parts Kit M-16 Ar320


  • Comes With a Spare Takedown Detent and Detent Spring
  • Each of the Touch Points is Finished for the Smoothest Functionality
  • The Spring Pins Are Made of Coiled Steel, Are Easy to Install, and Won't Creep Out


  • Some Fitting May Be Required

Doublestar is a Kentucky company that has been in business for over 25 years. It is a family company that produces an entire line of complete firearms with passion. They also specialize in parts and accessories for modern sporting rifles. Their lower parts kit focuses on top-quality components made entirely in the U.S.A.

The fire control group adheres to military specifications by being machined from heat-treated 8620 steel. All touch points are finished for the smoothest operation and crispest trigger pull. If you are sick and tired of creep or drag, this option is for you. All parts included in the kit are designed and manufactured to last for the entire service life of your firearm.

As a unique feature, Doublestar uses coiled steel spring pins instead of split roll pins. These are easier to install and are less likely to creep out again. The kit comes with a spare takedown detent and spring, as these are so easy to lose. The kit includes all parts needed to complete your lower and is covered by Doublestar's warranty.

Bottom Line

This is a great parts kit from a well-established family company. Its top features are the extra finishing on all the touching points and the coiled steel springs. The spare detent components are a great touch too.

2. CMMG - AR-15/M16 Lower Spring Kit


  • The Perfect Parts Kit for Repairs or to Keep Spare Springs Handy
  • All of the Parts Meet or Surpass Military Specs for Quality
  • Designed and Manufactured Right Here in the U.S.A. by a Family-Owned Company


  • Not the Cheapest Option

CMMG is run by four members of the Overstreet family. They founded the company in 2002 in Missouri. Since then, they have won a lot of respect in the black rifle market. This is partly because all of their modern sporting rifles, parts and accessories are made in the U.S.A. to high specifications.

The family backs this up with a guarantee against defects in material or workmanship for the life of each product. This lower receiver parts kit focuses on pins and springs. This makes it perfect as a parts kit for refurbishing or repairing an old lower receiver.

Every single part included either adheres to or surpasses military specifications for quality and reliability. If you have tried to replace parts in a modern sporting rifle or tried to build your own from scratch, you know how hard it is to keep the tiny springs and pins from flying or rolling away on you. This is a great backup kit to address just that problem. Also, the quality is hard to beat.

Bottom Line

This is one of the best quality parts kits on the market. The top feature is its rigorous adherence to military specifications. The fact that all of the parts are made right here in the U.S.A. is reassuring too.

3. Windham Weaponry Pkmwk Most Wanted Parts Kit


  • Designed and Made With Pride Right Here in the U.S.A.
  • The Perfect Backup Kit in Case of Sudden Part Failure
  • Comes With All of the Most Commonly Lost or Worn Out Parts


  • May Not Include All the Parts You Need for a Full Build

Windham Weaponry has an interesting story. Bushmaster, one of the most revered names in black rifles was bought out in 2006. The new owners decided to move the facilities out of Maine. The former owner of Bushmaster still owned the site, so, as soon as his non-compete clause expired, he hired many of the laid-off workers back to start a new project.

That project was successful and one of its fruits is this lower parts kit. Windham calls it their Most Wanted Parts Kit because it contains all the parts that most commonly go flying off or slip into some tiny crack never to be seen again.

It includes four pivot pin detents, four pivot pin detent springs, two safety detents, two safety detent springs, two firing pin retaining pins, two buffer detents, two buffer detent springs, two extractor springs, two extractor spring inserts, and two extractor O-rings. This is another option that is great to keep as a backup in case something goes missing during routine cleaning.

Bottom Line

This is a great parts kit to keep around in case something suddenly breaks or gets lost. The top features of this kit are the fact that it only comes with all the most commonly lost or worn out parts. It's also always nice to buy something made in the U.S.A.

4. Colt - Lower Receiver Parts Kit


  • Allows You to Choose Your Own Trigger and Pistol Grip
  • Comes With an Accu-Wedge to Minimize Jiggle and Improve Your Rifle's Accuracy
  • Colt-Branded Original Parts From and Made by One of the Nation's Most Storied Weapons Companies


  • Not the Cheapest Option
  • Suspiciously Indistinguishable From a Brownells Parts Kit

Colt is a legendary name in American firearms, and not just for M16-style rifles. The company has been around since 1855 and is based out of Connecticut. Although not as dominant as it once was, Colt still has some outstanding products on offer. This kit includes all the small parts you need to build or refurbish a lower receiver.

It does not come with a trigger group or a pistol grip. Colt has thrown in their proprietary Accu-Wedge, a rubber insert meant to tighten up the connection between receiver halves. As the name suggests, the Accu-Wedge should improve accuracy. Colt underscores that its pedigree as an original military supplier of the M16 means that its parts are rigorously up to spec and require minimal fitting.

This kit is meant for small-pin, mil-spec M16-style lower receivers. This is a great kit if, like most shooters, you still want a bit of flexibility on what trigger and pistol grip to get. Many shooters will also be reassured buying a parts kit from one of the most legendary companies in the modern sporting rifle field.

Bottom Line

If you are a huge Colt fan, this is the lower parts kit for you. The top features of this kit are the Accu-Wedge and the ability to choose your own pistol grip and trigger.

5. Brownells - AR-15/M16 Lower Receiver Kit


  • This Product is a Non-FFL Item so it is Easy for Anyone to Buy
  • Comes With a Fire Control Group so You Don't Need to Buy One Separately
  • The Receiver Ships With No Finish,so You Can Complete the Finishing Process Yourself


  • Jig Not Included
  • May Have Tooling Marks in the Mag Well

As I never tire of noting, Brownells-branded products are a great choice. As one of the nation's top firearm and firearm accessory retailers, the company has market data that many companies would kill for. Brownells uses this knowledge of what works, what is popular, and what is reliable to market a wide variety of excellent firearm solutions.

This lower receiver kit is no exception. This is considered an 80-percent lower receiver. The receiver itself, from Anderson Manufacturing, is forged from standard 7075-T6 aluminum alloy. This product is unique in that it ships with no finish, you will have to hardcoat or Parkerize it yourself.

Some milling is also required around the trigger group. This allows it to be a non-FFL product. It comes with a complete parts kit from DPMS, one of the biggest names in black rifles. The parts kit includes everything listed in the section above, including a hammer and trigger. Everything in the combo is made in the U.S.A. For the extra milling, you will need a jig, which is sold separately.

Bottom Line

If you are on a budget, you can't beat this Brownells lower parts kit. Its top features are the non-FFL status and its completeness, you don't even need to buy a fire control group.


Building your own M16 or repairing an old one is an interesting but difficult task. If you have the skills and bravery, it can be very rewarding, especially if you get top-quality parts. We're sure you'll find what you need on our list. Good luck with the build and have fun!

Michael Lutes is the managing editor and owner at Gun Mann. He is a veteran, gun enthusiast, 3 gun competitor, and 2a advocate. Mike has a passion for innovation and education across the industry to create great content, training, and insights from the best and brightest.

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