Best M16A2 Parts Kit (Full Overview and Review)

| Last Updated: June 3, 2021

An M16A2 parts kit is one of the most important products you need for building a quality M16A2 rifle.

There are dozens of options on the market and choosing the best one can be difficult.

Luckily, you can simply follow our guide to the best M16A2 parts kits.

Comparison of the Best M16A2 Parts Kit

  • Comes with an A2 style buttstock spacer.
  • The parts in this kit are very reliable and high-quality.
  • Ideal for customizing the buttstock of your AR style rifle.
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Are All Parts Kits The Same?

It can be very hard to verify the quality of an M16A2 parts kit. The best way, as usual, is to go with a proven product by a well-established, reputable manufacturer. Each part has its own specifications in material and manufacturing method which is otherwise very hard to verify. Not all parts kits are complete.

There are parts kits just for your upper receiver or lower receiver, and parts kits just to replace one category of parts, like the springs or trigger group. Some companies get a bit drunk on their own brand recognition and apply excess markup on their parts kits.

Companies like Brownells and Palmetto State Armory sell so many modern sporting rifle components that they have a wealth of knowledge on what works best. Buying parts kits marketed under their own brands is a great solution.

Are There Essential Pieces Not Included?

Parts kits generally include all the springs, pins, bolts and controls you need to get your build working. Some major components will not be included because the whole point of building your own modern sporting rifle is customizing some of the key components used.

Some of these components usually not included in a parts kit include the charging handle, the bolt carrier group, the trigger group, the barrel, barrel insert, and related components, the handguard, the stock, and the pistol grip.

Of course, these days, sighting options are usually not included. The top rail lets you choose whatever sighting options you prefer, whether aperture sights, reflex sights or a scope. Usually, the upper and lower receivers are also excluded from a parts kit. All this varies on the make and model of the parts kit in question. There is no strict and fast rule.

Building an M16A2 - What You Need to Know

It is important to know what you are getting with any given parts kit so that you don't end up missing some vital components when you want to go out shooting. The components are roughly divided into those for an upper receiver and those for a lower receiver.

Upper Receiver Parts Kit

Upper receiver parts kits are not as prevalent or easy to define as lower parts kits. Some upper receivers include a forward assist and a dust cover and some do not. This varies the number of parts necessary. A2 style upper receivers have a removable carry handle, while later variations stick to flat top rails.

Generally speaking, an upper parts kit will include components for a forward assist, which helps in case of a cartridge jam. It also includes components for a dust cover to keep foreign matter out of your receiver. Finally, it includes parts for a barrel nut and a forend grip retainer.

These hold the barrel and forend grip to the receiver. All together, these components include a forward assist, forward assist spring, and forward assist retaining pin, a dust cover, dust cover spring, and dust cover rod, forend grip retainer, forend grip retainer spring, and a barrel nut, barrel nut washer.

Lower Receiver Parts Kit

Lower parts kits are more common and more standardized than upper parts kits. A full lower parts kit will include various sets of parts. First, it will have an M16 Sear, sear spring and sear pin. The sear holds the firing pin in the cocked position.

Second, the kit will have a buffer detent and a buffer detent spring. Next, are the components for the pistol grip, including a pistol grip screw and a pistol grip screw washer.

Then there is the bolt catch assembly which holds your bolt open after firing the last round. The mag catch assembly holds your mag in place and drops it when you hit the release.

Also included are a front pivot pin, 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.

Review of the Best M16A2 Parts Kit

With so much to think about, save yourself the confusion and simply follow our guide to the best M16A2 parts kits available today.

Best Overall:  
Brownells - AR-15/M16 A2 Rifle Buffer Tube Assembly


  • Ships With an A2 Style Buttstock Spacer
  • The Parts Included in this Kit are Extra Reliable and High-Quality
  • Perfect for Customizing the Buttstock of Your Modern Sporting Rifle


  • Missing a Groove for a Retention Pin

Brownells benefits from its position atop the firearms, parts and accessories market. All those sales across the country add up to a vast wealth of market information. Brownells uses this exclusive knowledge to build many of its own parts and firearms, which are usually very successful and reliable. This buffer tube assembly is a great example.

It includes all the parts you need to mount whatever buttstock you choose to your AR-style lower receiver. This kit is a great choice if you want to convert your stock, for example, by switching to a fixed rifle stock. All the parts that are included are made from the best materials and machined to exacting tolerances.

This helps to ensure the smooth function and long-term reliability of your build. This kit comes with a buttstock spacer that is designed to work specifically with A2-style rifle stocks. All of the parts included meet standard mil-spec requirements. Installation instructions are included. If you have a working modern sporting rifle but just want to experiment with buttstock options, this is the parts kit for you.

Bottom Line

Brownells is another unbeatable manufacturer in the modern sporting rifle market. The top features of this kit are the A2 style buttstock spacer, the customizability, and the high-quality parts. If you want to try switching out your buttstock, you can't beat this parts kit.

2. Colt - Lower Receiver Parts Kit


  • Lets You Custom-Select Your Trigger Group and Pistol Grip
  • Comes With All the Small Parts You Need to Build Your Lower
  • Ships With Colt's Accu-Wedge to Reduce Jiggle Between Upper and Lower


  • Incredibly Similar to a Kit Offered Under the Brownells Brand

Headquartered in Connecticut, Colt is one of the most legendary names in American firearms. Their sun may have set in recent years, but I, for one, feel good when I buy from Colt, knowing that I'm helping an icon that's been around since 1855 stay in existence.

Who knows, maybe one day they will bounce back, stranger things have happened. All that aside, Colt still does make some very fine products, if not always the most affordable or the best value for money.

All things considered, this lower receiver parts kit is a great option. It comes with all the small parts you need to build a small-pin AR-style lower receiver. It does not include 'big parts', such as a trigger module or pistol grip. You are left to choose those separately according to your tastes.

This is also a great kit for refurbishing an old lower to get back some of the lost reliability and accuracy. Colt ships this kit with their proprietary Accu-Wedge, a rubber insert that sits inside the receiver behind the take-down pin. Its purpose is to prevent any annoying jiggle between the upper and lower receivers.

Bottom Line

If you have a sentimental attachment to the Colt brand, this is a great lower parts kit for you. Its top features are the Accu-Wedge and the ability to custom select your own trigger group and pistol grip.

3. PSA 20" A2 Freedom Rifle Kit


  • All of the Parts Conform to Mil-Specs and are Made in the USA
  • Backed up by Palmetto State Armory's Industry-Leading Unlimited Lifetime Warranty
  • Comes With Everything Needed for Building Your Own M16, Except the Lower Receiver


  • May be Poorly Packaged or Arrive With Scuffs

Palmetto State Armory is one of the leading distributors of firearms and firearm accessories. They have extensive market research on what works, what is popular and what is reliable. Using this knowledge, they market many of their own products which are often the best value on the market. This rifle kit is no exception.

It comes with a 20-inch Chrome moly vanadium steel barrel with a standard 1:7 twist rate. The barrel has an A2 profile and is finished in nitride. The barrel is paired with an M4 barrel extension and a rifle length gas system. The front sight base is F-marked. The barrel is also decorated with a classic handguard and an A2 flash hider.

The upper receiver is a very standard forged 7075-T6 A3 design. It is mil-spec and hard coat anodized in black for protection. As you would expect, it is made in the USA. The bolt is manufactured from shot-peened Carpenter 158 tool steel. The outside of the carrier is parkerized. The lower build kit has everything you need except the lower receiver itself.

Bottom Line

PSA is always a great, no-brainer option. The top features of this kit are the completeness, the warranty, and the mil-spec design. No matter what you need from a rifle kit, this option will do it for you.

4. PSA Upper Build Kit and Classic Lower Parts Kit Combo


  • Ships With All the Small Parts Needed to Build a Custom M16
  • Backed up by Palmetto State Armory's Outstanding Unlimited Lifetime Warranty
  • The Hammer and Trigger Springs are Black Oxide Coated for Corrosion Resistance


  • The Trigger has a Lot of Take-Up and a Heavy Pull Weight

If you haven't gotten the picture by now, Palmetto State Armory parts kits, and pretty much everything else they produce, are outstanding quality for the price tag. Customer service is good, the unlimited lifetime warranty is good, and most shooters come away very satisfied. This option is a unique upper and lower receiver combo parts kit.

Although it does not come with a buttstock or either the upper or lower receivers themselves, it includes pretty much every other component you need for a complete A2-style modern sporting rifle build. All the parts are designed, made and finished right here in the USA. The kits are compiled at PSA's facility in Columbia, South Carolina.

The kit has been updated to include hammer and trigger springs that are coated in black oxide. If you are making your own custom build but you don't want to fuss about finding different kits or different versions of selector switches, triggers, and mag releases, we're sure that you will be satisfied with this parts kit.

Bottom Line

This is another invaluable parts kit from Palmetto State Armory. The top features of this kit are the fact that it includes a full set of AR parts, the springs are oxide coated, and everything is covered by PSA's unlimited warranty.

5. Palmetto State Armory A2 Freedom Rifle Lower Build Kit


  • One of the Best Values for Money Options on the Market Today
  • Comes With Everything You Need to Custom Build Your Lower Receiver
  • Backed up by Palmetto State Armory's Unlimited Lifetime Warranty for Materials and Manufacture


  • May Require Fitting

We like the specs of Palmetto State Armory's kits so much, that they have earned multiple places on our list.

The well thought out design and high-quality construction of pretty much all the PSA branded firearms and components make them a great default, no-brainer option for any modern sporting rifle or custom build. A quick survey of feedback that Palmetto State Armory receives and how often their products are recommended shows that the company is truly a market leader.

If you have a spare stripped lower receiver laying around, this kit has everything you need to turn it into a fully functional lower receiver. That includes an A2 stock with a plastic latch, a rifle length buffer tube, a buffer and a spring. Most importantly, it comes with PSA's popular lower parts kit.

The kit has all the internal components, like the trigger group and fire selector, that you need to construct a working lower receiver. All the components are built to high tolerances using top quality materials. This kit has proven its reliability over the years.

Bottom Line

This is the perfect option if you're on a budget. The top features of this kit are the fact that it comes with all the small components you need and PSA's excellent warranty. You can't really go wrong with a PSA kit.

How to Build an M16A2

Below is a video guide to building your own M16A4 rifle without tools or a vise. The difference between an A2 and an A4 is mainly that an A2 has a fixed carry handle whereas an A4 has a Picatinny top rail.

First, collect the parts into their respective component groups. Start by building the trigger group assembly. Mount the hammer spring, trigger spring and disconnector spring.

Once you have the disconnector inserted, drop the trigger assembly into the lower. Align the pin holes and punch the pins in. Do the same for the trigger guard. Next, slip in the mag catch and push in the release button. Screw down the catch.

Next, assemble the bolt catch assembly, you will need pliers. After that comes the safety, grip, rear takedown pin, and receiver extension. The safety detent goes in first, then the pistol grip. The takedown detent and the buffer retainer go in their slots in a similar way.

Then you can twist in the receiver extension while depressing the buffer retainer. Don't forget your A2 spacer. The front takedown pin is always tricky to do without losing the detent. Use pliers, hold the detent down with an Exacto-knife. Slide the front takedown pin in along, removing the knife when possible.

Next, cock the hammer to push the buffer spring and extension into the tube. Finally, make sure it works and head to the range!


Parts kits are a complex topic and choosing the best one depends on knowing what kind of build you want to make and how much of it you want to customize. Choices abound, but we're sure that you will find the parts kit for you in our guide. As always, shoot safe and have fun.

Josh Lewis the managing editor at Gun Mann and when he isn't writing about guns he is more than likely tinkering with them. He also enjoys hunting, fishing and spending time outdoors. As a lifelong gun owner he knows his stuff!

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