How to Assemble an AR-15 Lower – Step-by-Step

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Jason Schaller

Let’s assemble an AR-15 lower! An AR-15 lower receiver assembly might sound intimidating, but it’s easier than it looks. This guide breaks down every step to build your AR-15 lower from scratch—no guesswork, no stripped threads, and no flying springs. Whether it’s your first build or your tenth, this walkthrough helps you get it done right the first time. Let’s assemble an AR-15 lower

TL;DR

• Step-by-stepAR-15 lower receiver assembly guide

• Works for AR-15 and AR-10 lowers (bolt catch differs)

• Clear video timestamps for every part

• Covers buffer tube, stock, trigger group, pins, and safety

• Great for first-time builders or rebuilders

  
  

What tools do you need to assemble an AR-15 lower?

• Bench block or vise

• Armorer’s wrench

• 1/16” and 3/32” roll pin punches

• Small hammer

• Needle-nose pliers

• Flathead screwdriver

• Allen wrenches (for A2 grip)

Optional:

• Pivot pin installation tool

• Real Avid Armorer’s Master Kit

How do you install the AR-15 bolt catch?

Video Timestamp: 0:34

Start with the bolt catch. Align the parts and gently drive the roll pin through. Use a bench block to avoid scratches.

How do you install the AR-15 trigger guard?

Video Timestamp: 2:57

Line up the guard with the receiver ears. Support it fully before tapping the roll pin in place—these tabs crack easily.

How do you install the rear takedown pin on an AR-15?

Video Timestamp: 4:08

Insert the detent and spring in the receiver’s rear channel. Push in the takedown pin from the left side until it locks.

How do you assemble and install a collapsible stock?

Video Timestamp: 5:35

Slide in the latch spring and locking pin. Compress the latch and push the stock onto the buffer tube until it locks.

How do you install a collapsible stock on an AR-15 lower?

Video Timestamp: 7:08

Thread the buffer tube in, capture the detent and spring, and tighten the castle nut. Ensure the end plate locks in.

How do you install an A2 stock on an AR-15?

Video Timestamp: 10:13

Slide the A2 stock over the receiver extension. Align the buffer retainer and secure with the long bolt.

How do you install the front takedown pin?

Video Timestamp: 12:18

Insert the detent and spring. Push in the takedown pin while compressing the spring. A pivot pin tool helps here.

How do you install the AR-15 magazine catch?

Video Timestamp: 13:45

Insert the catch and spring. Thread in the mag release button and spin the catch until it sits flush with the receiver.

How do you install the AR-15 trigger spring and trigger?

Video Timestamps: 15:15 + 16:21

Place the trigger spring over the trigger. Install it and the disconnector into the receiver and pin them down.

How do you install the safety selector and pistol grip?

Video Timestamp: 18:05

Drop the selector into the receiver. Insert the detent and spring into the grip. Attach and tighten the grip.

How do you install the hammer spring and hammer?

Video Timestamps: 20:03 + 20:29

Install the spring onto the hammer with the legs properly oriented. Push the hammer down and insert the pin.

How do you install the buffer retainer and buffer tube?

Video Timestamp: 22:11

Insert the retainer spring and detent. Thread in the buffer tube just enough to hold the retainer. Install the buffer and spring.

How do you perform a function check on your AR-15 lower?

Video Timestamp: 22:56

Ensure the trigger and safety work correctly. Hammer should release on “fire,” not on “safe,” and reset after cycling.

What should you check after assembling an AR-15 lower?

• Confirm selector blocks trigger

• Check hammer and trigger movement

• Test mag release

• Verify takedown pins move freely

• Ensure buffer tube and stock are solid

The bolt catch always gave me the most grief when I was learning. If you scratch the finish here, it’s because you didn’t stabilize it right.

— Jason Schaller

Frequently Asked Questions About Assembling an AR-15 Lower

What tools do I need to assemble an AR-15 lower?

You’ll need a small hammer, roll pin punches, needle-nose pliers, an armorer’s wrench (optional), and a bench block. A vice and lower receiver vise block help but aren’t required.

Can I assemble an AR-15 lower without special tools?

Yes, but it’s harder. You can use improvised tools like a flathead screwdriver and punch alternatives, but a proper roll pin punch set and bench block make the job safer and cleaner.

What’s the hardest part to install on an AR-15 lower?

The bolt catch roll pin is often the trickiest due to its tight space and risk of scratching the lower. A starter punch or tool like the Real Avid punch set makes it easier.

Do I need to install the buffer tube before the stock?

Yes. The buffer tube must be installed first, as the stock locks into it. The detent and spring under the tube must also be seated correctly during install.

What’s different between building an AR-15 and an AR-10 lower?

Most steps are the same, but the AR-10 uses a threaded bolt catch instead of a roll pin, and some internal dimensions may vary depending on the manufacturer.

Wrap-Up

Assembling an AR-15 lower might seem daunting, but it’s one of the most satisfying parts of building a rifle. Each pin, spring, and detent has its place—and once it’s all together, you’ll know your firearm inside and out. Whether you’re doing a custom build or replacing parts, this guide takes the guesswork out and gets you across the finish line with confidence.

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Original Content by The Rogue Banshee / My Rogue Solutions LLC.
Credit: Jason Schaller
Email: jschaller@trb.fyi

About the Author: Jason Schaller is a former FFL holder and founder of Eagle Eye Shooters Supply in Helena, MT, where he provided professional gunsmithing services and guided customers on all aspects of firearms ownership. Today, he teaches DIY gunsmithing at The Rogue Banshee and serves as a Chief Instructor at Freedom Crew University. With over a decade of hands-on professional experience with firearms and nearly 30 years in IT, Jason also holds top cybersecurity certifications including CISSP, CISA, and CRISC. When he’s not geeking out, he’s helping others build self-reliance, critical thinking, and firearms proficiency through real-world content.

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