Buffer · Baseline weight
H2 Buffer (4.6-4.7 oz)
Standard H2 buffer weight for most suppressed AR-15s. Adds mass to slow the bolt carrier and reduce felt recoil.
- ✓Good starting weight for 5.56
- ✓Fine-tune with gas-system-buffer-tuning guide
BeginnerAR-15Builds
How to Build an AR-15: Complete Parts List & Step-by-Step Guide (2026)
Complete parts list, tools, and step-by-step assembly. Your first build should be dead simple: quality parts, zero custom headspace work, and a clear upgrade path.
The short version
- 1) Acquire a stripped lower from your local FFL. Buy online and ship to them for transfer, or purchase in-store.
- 2) Install a quality lower parts kit (LPK), your chosen trigger, grip, and stock/brace. Use the Lower Parts Quality Guide for vetted kits.
- 3) Attach a complete upper from PSA, Aero Precision, BCM, or Geissele based on your price tier. Mate it to your lower, function check, and head to the range.
First time building? Review the Common Beginner Mistakes guide before you start, it'll save you time and frustration.
Complete AR-15 Parts List
Every component you need to build an AR-15 from a stripped lower receiver. We recommend buying a complete upper assembly (covered in Step 3) to skip headspace and gas system complexity, but this list covers both paths.
Lower Receiver Parts
- Stripped lower receiver (FFL transfer required)
- Lower parts kit (LPK) or individual components:
- - Trigger assembly (hammer, trigger, disconnector, springs)
- - Safety selector + detent + spring
- - Magazine catch + button + spring
- - Bolt catch + plunger + spring + roll pin
- - Pivot pin + detent + spring
- - Takedown pin + detent + spring
- - Trigger guard + roll pin
- Pistol grip + screw + lock washer
- Buffer tube (carbine or rifle length)
- Castle nut + end plate
- Buffer (H, H2, or H3 for carbine)
- Buffer spring
- Stock (rifle) or brace (pistol)
Upper Assembly (Complete or Build)
Recommended: Buy a complete upper (PSA, Aero, BCM) to skip this list.
- Upper receiver (stripped or assembled)
- Barrel (5.56 NATO, 10.5"-20")
- Barrel nut
- Gas block (low-profile or A-frame)
- Gas tube (carbine, mid, or rifle length)
- Handguard (M-LOK or KeyMod)
- Muzzle device (flash hider, brake, or comp)
- Bolt carrier group (BCG)
- Charging handle
- Forward assist assembly
- Ejection port cover assembly
Beginner Path: Complete Upper + Lower Build
For your first build, buy a factory complete upper (includes barrel, gas system, BCG, and charging handle pre-assembled). This eliminates headspace checks, gas port alignment, and barrel timing. You only need to build the lower receiver, which requires the left column above plus basic tools. See Step 3 for tier recommendations.
Step 1: Buying a Stripped Lower Receiver (FFL Transfer)
The lower receiver is the regulated part. Order a stripped lower online from a reputable manufacturer and ship it to your local FFL for transfer, or buy one directly at the shop. Bring ID, complete the 4473, and keep the receipt with your serial number for records.
Avoid bargain-bin or polymer lowers (unless it's a reinforced KP-15). Stick with forged 7075-T6 from brands like Aero, BCM, Geissele, or PSA. Check that the takedown pins move smoothly before you leave the counter.
NFA and pistol brace basics
Under federal law, a rifle with a barrel under 16 inches or overall length under 26 inches is a Short-Barreled Rifle (SBR) and regulated under the NFA. You need an approved Form 1 or Form 4 before assembling or possessing an SBR with a stock. If you want to run a sub-16" barrel without NFA paperwork, configure it as a pistol (no stock) or register it.
Pistol braces are currently permitted on AR pistols under the latest federal guidance, but you must still follow state laws and avoid adding a stock unless you have SBR approval. Easiest compliance path for beginners: stick with a 16"+ complete upper unless you have paperwork in hand or are staying in pistol configuration.
Important: A stripped lower receiver can be built into either a pistol or rifle configuration, you decide when you assemble it. However, a firearm originally manufactured or sold as a rifle can only ever be a rifle or SBR, never a pistol. This is why starting with a stripped lower gives you maximum flexibility.
Step 2: Installing the AR-15 Lower Parts Kit & Trigger
Tools needed: Armorer's wrench, punch set, torque wrench (in-lb and ft-lb), vise block, and a clean workspace. See our AR Tools Guide for the complete list and recommendations. Torque specs and threadlocker guidance are in the reference section below.
A solid lower parts kit gives you reliable springs, detents, and controls. Avoid no-name kits; pick PSA, Aero, BCM, SOLGW, or Forward Controls–sourced components. Reference the Lower Parts Quality Guide for vetted options.
Select the trigger that matches your mission (mil-spec for duty durability, or a known single-stage/2-stage upgrade like ALG ACT, Geissele SSA, or LaRue MBT). Add an ergonomic grip you like and a stock or brace that locks up tight. Torque the castle nut to spec and stake it; this prevents loosening over time.
Start with a carbine H2 buffer for most 16" 5.56 setups, then fine-tune only after live-fire. See the Gas System & Buffer Tuning guide if you need to adjust buffer weight or springs.
For a step-by-step visual walkthrough, check out Pew Pew Tactical's lower assembly guide, it has detailed photos for every step.
Lower essentials to keep it simple
Starter lower picks that avoid no-name parts: a quality LPK, proven trigger, and a solid adjustable stock.
LPK · Reliable springs & detents
CMMG Lower Parts Kit
Complete mil-spec lower parts kit with all pins, springs, and detents. Quality baseline for any build.
- ✓Detents and springs that fit correctly
- ✓Keeps your trigger choice open
Trigger · Two-stage value
LaRue MBT-2S Trigger
Precision-machined two-stage AR trigger with crisp break
- ✓Predictable wall and break
- ✓Outstanding value for performance
Stock · Tight lockup
Magpul MOE SL Carbine Stock
Streamlined MOE stock with improved cheek weld
- ✓Low-profile geometry
- ✓Secure fit on mil-spec tubes
Receiver extension · Mil-spec
Mil-Spec Buffer Tube Kit
Standard mil-spec carbine buffer tube assembly with buffer, spring, and end plate.
- ✓Mil-spec diameter for stock compatibility
- ✓Includes end plate and castle nut
Brace · Pistol builds
SB Tactical SBA5 Pistol Brace
5-position adjustable pistol brace with integral QD sling socket and improved ergonomics
- ✓Adjustable for length of pull
- ✓Pairs with mil-spec buffer tube
Purchasing through these links may generate a commission at no extra cost to you. Verify compliance for any serialized parts and follow local/state laws.
Step 3: Choosing a Complete Upper (PSA vs Aero vs BCM vs Geissele)
Buying a factory-complete upper skips headspace checks, gas-port guesswork, and alignment issues. Pick the tier that matches your budget and intended use, then verify it includes a BCG and charging handle or add those from the same brand. Before your first range trip, lube generously, perform a function check, and verify gas block screws are torqued and secured. Start with quality magazines (Magpul, Lancer, Okay/SureFeed) to rule out mag-related malfunctions.
Entry · Budget but vetted
PSA Premium/CHF Complete Upper
PSA's Premium/CHF lines use FN-made barrels and solid QC for the price. Look for mid-length gas and pinned gas blocks when available.
- ✓Stick to complete uppers with FN cold hammer-forged barrels
- ✓Solid QC for the money and great warranty support
- ✓Avoid mystery clearance batches and no-name barrels
Mid-range · Balanced
Aero Precision Complete Upper
Clean machining, consistent gas, and easy parts support. Choose 4150 CMV or stainless barrels and pinned gas blocks when possible.
- ✓Choose pinned gas blocks and 4150 CMV or stainless barrels
- ✓Good balance of price, machining quality, and parts availability
- ✓Plays nicely with most lowers without fitment drama
Duty-grade · Proven
BCM Complete Upper
Conservative gas ports, excellent staking, and robust QC make BCM a reliable choice for high round counts. Opt for BFH barrels for maximum life.
- ✓Choose BFH (hammer-forged) for maximum barrel life
- ✓Proven reliability with conservative gas tuning
- ✓Ideal for training-heavy schedules
Top tier · Premium
Geissele Super Duty Complete Upper
Geissele's Super Duty uppers feature their proven reliability rail, chrome-lined barrels, and impeccable fit/finish. Available in 11.5", 12.5", 14.5", and 16" configurations.
- ✓Available in 11.5", 12.5", 14.5", and 16" configurations
- ✓Premium triggers, tight tolerances, excellent fit/finish
- ✓Built for hard use with strong factory support
Purchasing through these links may generate a commission at no extra cost to you. Confirm barrel length and muzzle device compliance (pin-and-weld or NFA paperwork) before ordering.
Not sure which barrel length to pick? Our barrel length guide breaks down velocity, dwell time, and handling from 10.5" to 20".
Handpicked Complete Uppers
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Step 4: Function Check Your Build
Before loading any ammunition, verify your rifle functions correctly. Clear the weapon visually and physically: lock the bolt back and confirm the chamber is empty.
Warning: Never drop the hammer on your lower receiver without the upper installed. The hammer striking the bare receiver can crack the aluminum over time. Always complete your upper/lower assembly before testing trigger function.
- Trigger & hammer reset: With the safety OFF, pull the trigger and hold it. Manually cycle the charging handle to reset the hammer. Release the trigger slowly, you should feel and hear a click as the disconnector releases the hammer to the trigger sear.
- Safety selector: Cock the hammer (cycle the charging handle). Flip the safety to SAFE. Pull the trigger, nothing should happen. Flip to FIRE and pull, the hammer should fall.
- Bolt catch: Lock the bolt back using the bolt catch. It should hold firmly. Press the bolt release, the bolt should snap forward cleanly.
- Magazine insertion: Insert an empty magazine. It should lock in with a solid click. Press the magazine release, it should drop free without sticking.
If any step fails, diagnose before live fire. Common issues include improperly installed safety detent springs, trigger pin walk, or a misaligned bolt catch. Double-check your lower parts installation.
Quick Reference: Torque Values & Threadlocker
Torque Specs
- Castle nut: 35–40 ft-lbs (then stake)
- Barrel nut: 30–80 ft-lbs (varies by design)
- Muzzle device: 15–20 ft-lbs
- Gas block screws: 25–35 in-lbs
- Grip screw: 40–45 in-lbs
- Optic mount: Per manufacturer (usually 15–25 in-lbs)
Threadlocker Guide
- Blue Loctite (242/243): Gas block screws, optic mounts, grip screw, buffer tube
- Rocksett: Muzzle devices (for suppressor use or pinned devices)
- None: Castle nut (stake instead), barrel nut, takedown pins
Clean threads with degreaser before applying. Blue Loctite is removable with heat; Rocksett requires soaking.
Next moves
After assembly, run a 300–500 round shakedown with quality ammo and mags. Track malfunctions, then adjust buffer weight or springs only if needed, see the Gas System & Buffer Tuning guide for diagnostics.
When you're ready to add glass, check out the Optic Selection Matrix to find the right optic for your use case, then follow the Optic Mounting Basics guide for proper installation. Planning to run suppressed? Start with the Suppressor Compatibility Basics guide.
Legal disclaimer
You are responsible for complying with all federal, state, and local laws, including NFA rules, pistol brace guidance, and transfer requirements. This guide is informational only and is not legal advice, consult an attorney or your FFL if you have questions about what is lawful in your jurisdiction.
First AR-15 Build FAQ
▶How much does it cost to build an AR-15?
A quality first AR-15 build typically costs $600-1200 depending on tier. Entry-level (PSA parts): $500-700. Mid-range (Aero Precision): $700-900. Duty-grade (BCM): $1000-1400. Top tier (Geissele): $1500+. These prices include stripped lower, LPK, trigger, stock, buffer kit, and complete upper with BCG and charging handle.
▶Is it cheaper to build or buy an AR-15?
Building is usually 10-20% cheaper at the mid-range and up, plus you get exactly the parts you want. At the entry level, complete rifles from PSA or S&W M&P Sport can match DIY pricing. The real advantage of building is customization: you choose every component rather than replacing factory parts later.
▶What tools do I need to build an AR-15?
Essential tools: armorer's wrench, punch set (brass and steel), torque wrench (in-lb and ft-lb), vise block, hammer, and blue Loctite. Optional but helpful: pivot pin installation tool, roll pin holders, and a dedicated AR lower vise block. Total tool investment is typically $50-150 for quality basics.
▶Do I need to do a background check to build an AR-15?
Yes. The stripped lower receiver is the serialized, regulated part that requires an FFL transfer and 4473 background check. All other parts (upper, barrel, trigger, stock) are unregulated and can be shipped directly to you. This is federal law, state laws may have additional requirements.
▶What is the difference between a pistol and rifle AR-15?
Barrel length and stock type determine classification. A rifle has a barrel 16" or longer with a stock. A pistol has a barrel under 16" with a brace (not a stock). An SBR (Short Barreled Rifle) has a barrel under 16" with a stock, requiring NFA registration. A stripped lower can be built into either configuration, you decide at assembly.
▶PSA vs Aero vs BCM: which complete upper should I buy?
PSA (entry, $300-400): Good QC, FN CHF barrels on Premium line, great for budget builds. Aero (mid-range, $400-600): Better machining, more consistent, good value. BCM (duty-grade, $700-900): Proven reliability, conservative gas tuning, excellent for hard use. Choose based on budget and intended use: all three are reliable when properly assembled.
▶Is it legal to build your own AR-15?
Yes, building an AR-15 for personal use is federally legal without a manufacturing license. The lower receiver requires FFL transfer and background check, but assembly is legal. You cannot build with intent to sell without an FFL. State and local laws vary: California, New York, and several other states have additional restrictions on features, registration, and serialization requirements.
▶What is the 26 inch rule for AR-15s?
Federal law requires AR pistols to have an overall length (OAL) of at least 26 inches to legally add a vertical foregrip without NFA registration. OAL is measured from end of buffer tube (or brace in folded position) to end of barrel threads, excluding muzzle devices unless permanently attached. Below 26 inches with a VFG = AOW requiring NFA tax stamp.
▶What parts do I need to build an AR-15?
For a complete AR-15 build from a stripped lower, you need: 1) Stripped lower receiver (FFL required), 2) Lower parts kit with trigger, safety, mag catch, bolt catch, pins, and springs, 3) Pistol grip with screw and lock washer, 4) Buffer tube, castle nut, end plate, buffer, and buffer spring, 5) Stock or brace, 6) Complete upper assembly (barrel, gas system, handguard, BCG, and charging handle pre-assembled). Most beginners buy a factory complete upper from PSA, Aero, or BCM to avoid headspace and gas system complexity.
▶How long does it take to build an AR-15?
A first-time lower build with a complete upper typically takes 2-4 hours, including time to watch reference videos and work carefully. Experienced builders finish a lower in 30-60 minutes. Building the upper from scratch adds 1-2 hours for barrel installation, gas system alignment, and handguard mounting. Budget 3-4 hours total for your first build and work on a clean, well-lit surface.
▶What is the best caliber for a first AR-15 build?
5.56 NATO/.223 Remington is the best caliber for a first AR-15 build. Ammo is widely available and affordable ($0.30-0.50/round), recoil is manageable for new shooters, and parts compatibility is universal. A 5.56 NATO chamber safely fires both 5.56 and .223 ammo. Once you have a reliable 5.56 platform, you can add caliber variety later with a dedicated .300 Blackout or 6.5 Grendel upper.
Complete Your Build
Essential accessories to round out your setup
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Next Step
Ready to continue? Here's the recommended next guide:
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ABAuthor
Avid shooter with 9+ years of experience including competition shooting. Built 10+ AR-pattern rifles and several handgun platforms for home defense, competition, and suppressed night shooting.
9+ years shooting experienceCompetition shooterBuilt 10+ AR-pattern rifles
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