Looking for the best AR-15 build kit? PSA is the only major brand selling actual bundled kits (upper + LPK + buffer kit + stock). For Aero Precision, BCM, and Geissele, you buy a complete upper and lower parts separately. We've ranked the best build at each tier from $450 to $1,800 with exact parts lists, total costs, and the trigger upgrade you should add to each one.
Best Budget ($615 total): PSA CHF complete upper ($349) + CMMG LPK ($30) + LaRue MBT-2S trigger ($115) + buffer kit + stock + stripped lower. PSA also sells bundled kits ($450-550) if you want one SKU.
Best Mid-Range ($845 total): Aero M4E1 complete upper ($400-550) + Aero LPK no FCG ($25) + LaRue MBT-2S ($115) + buffer kit + Magpul stock + M4E1 lower.
Best Duty-Grade ($1,100 total): BCM complete upper ($799) + CMMG LPK ($30) + BCM Gunfighter stock + buffer kit + stripped lower.
Best Premium ($1,600 total): Geissele Super Duty upper ($1,199, includes REBCG) + Geissele LPK (includes SSA trigger + Super 42 spring) + stripped lower.
Every build requires a stripped lower receiver ($40-100) purchased separately through FFL. See our step-by-step build guide for assembly instructions.
An AR-15 build kit is a bundle of parts for assembling a rifle without buying a complete factory gun. The stripped lower receiver (the only serialized part) must be purchased separately through an FFL dealer with a background check.
Reality check: PSA (Palmetto State Armory) is the only major brand selling actual all-in-one build kits. Aero Precision, BCM, and Geissele sell complete uppers and lower parts as separate purchases. Most builders buy a complete upper and source lower parts individually. The term "build kit" in this guide refers to three things:
Upper + LPK + buffer kit + stock + grip in one SKU. PSA is the only major brand offering this. Add a stripped lower and you are done.
$450-$550
Lower parts kit + buffer kit + stock + grip. No upper included. Buy separately when you want to mix and match tiers.
$80-$300
Just the small parts: trigger, safety, mag catch, bolt catch, springs, detents, and pins. No buffer kit, stock, or grip.
$30-$120
Every part for a complete, range-ready rifle at each budget. Click any item to buy.
PSA also sells bundled kits ($450-550) with upper + LPK + buffer kit + stock in one SKU if you want fewer boxes to track.
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.
Complete mil-spec lower parts kit with all pins, springs, and detents. Quality baseline for any build.
Precision-machined two-stage AR trigger with crisp break
Standard mil-spec carbine buffer tube assembly with buffer, spring, and end plate.
Streamlined MOE stock with improved cheek weld
Budget-friendly mil-spec lower with blank left side for custom engraving. Best value entry point for AR builds.
Verify the Aero upper includes BCG and charging handle before ordering. "Complete" means with BCG/CH. "Assembled" means barreled only.
Clean machining, consistent gas, and easy parts support. Choose 4150 CMV or stainless barrels and pinned gas blocks when possible.
Lower parts kit without trigger group for those upgrading to aftermarket triggers. All other parts included.
Precision-machined two-stage AR trigger with crisp break
Standard mil-spec carbine buffer tube assembly with buffer, spring, and end plate.
Compact carbine stock with friction lock and sling attachment
Most popular upgrade lower receiver. Forged 7075-T6 with integrated trigger guard, threaded bolt catch pin, and upper tension screw.
The BCM upper is the heart of this build. Conservative gas ports mean softer recoil, less carbon, and longer part life.
Conservative gas ports, excellent staking, and robust QC make BCM a reliable choice for high round counts. Opt for BFH barrels for maximum life.
Complete mil-spec lower parts kit with all pins, springs, and detents. Quality baseline for any build.
Precision-machined two-stage AR trigger with crisp break
Standard mil-spec carbine buffer tube assembly with buffer, spring, and end plate.
Lightweight minimalist carbine stock
Duty-grade forged lower from BCM with enhanced features and excellent QC. Trusted by professionals.
The Geissele LPK ($275) includes the SSA trigger, Super 42 braided buffer spring, and all lower small parts. Buffer tube, stock, and grip are extras you pick.
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.
Two-stage match trigger
The A5 system uses a rifle-length buffer tube with intermediate buffer weights for smoother cycling and improved reliability.
Enhanced carbine stock with angled cheek weld and battery storage
Most popular upgrade lower receiver. Forged 7075-T6 with integrated trigger guard, threaded bolt catch pin, and upper tension screw.
Already have a complete upper? These standalone lower parts kits are ranked by spring quality, detent reliability, and included trigger. The LPK is where cheap kits cause the most problems: weak detent springs, rough trigger pulls, and missing parts.
Standalone lower parts kits for when you already have a complete upper or want to mix and match. Ranked by springs, detent quality, and included trigger.
Complete mil-spec lower parts kit with all pins, springs, and detents. Quality baseline for any build.
Lower parts kit without trigger group for those upgrading to aftermarket triggers. All other parts included.
Premium lower parts kit with enhanced components throughout. SOLGW quality at every contact point.
Complete mil-spec lower parts kit with A2 grip and Magpul trigger guard.
Chrome-lined, cold hammer forged (CHF) barrels last 20,000+ rounds. Nitride-treated barrels are cheaper and accurate but wear faster (10,000-15,000 rounds). PSA uses FN CHF barrels (same supplier as military contracts). Avoid kits that do not specify barrel treatment.
Mil-spec rated springs are non-negotiable. Weak detent springs cause the safety selector and takedown pins to walk out under recoil. CMMG, Aero, and BCM all use properly spec'd springs. If a kit does not name the LPK manufacturer, assume the springs are garbage.
Mid-length gas on 16" barrels is the modern standard (softer recoil, less fouling than carbine-length). Carbine gas on 10.5-14.5" barrels. Avoid 16" barrels with carbine gas, they are over-gassed and beat up the rifle. BCM's conservative gas port sizing is the gold standard.
Carpenter 158 or 9310 steel bolt, MPI (magnetic particle inspected) and HPT (high pressure tested). These are the minimum specs. Phosphate coating is standard, nitride is fine, nickel boron is easier to clean. Geissele's nanoweapon coating is the premium tier.
Weak detent springs: The #1 issue with cheap LPKs. The safety selector will not engage firmly, or takedown pins walk out under recoil. Fix: replace springs from a quality LPK (CMMG kit is $30).
Gritty mil-spec trigger: Every kit under $900 ships with an 8-9lb gritty trigger. This is normal, not a defect, but it makes shooting less enjoyable. Fix: upgrade to a quality trigger (LaRue MBT-2S at $115 is the standard recommendation).
Missing small parts: Budget kits sometimes ship without a trigger guard roll pin, buffer retainer, or detent. Inventory every part before you start building. Cross-reference against the complete parts list in our build guide.
Over-gassed uppers: Cheap complete uppers often have oversized gas ports. Symptoms: excessive recoil, blown primers, accelerated wear. BCM specifically addresses this with conservative port sizing. For other brands, an adjustable gas block is the fix.
No BCG or charging handle: Some "complete" uppers do not include a BCG or charging handle, especially from Aero. Always check the listing description. Budget $80-150 extra if the upper is barreled only.
The single biggest improvement to any AR-15 build. If your kit came with a mil-spec trigger, these are the upgrades worth the money. See our full trigger guide for detailed comparisons.
If your LPK comes without a trigger (or has a mil-spec trigger), these are the upgrades worth the money. A good trigger is the single biggest improvement to any AR-15 build.
Affordable combat trigger with polished mil-spec components. Smooth 6lb pull without creep.
Precision-machined two-stage AR trigger with crisp break
Two-stage match trigger
The most common approach among experienced builders: buy a BCM or Aero complete upper, pair with a CMMG LPK ($30), LaRue MBT-2S trigger ($115), Magpul MOE SL stock ($55), and a mil-spec buffer tube kit ($35). Total lower build: ~$235. Better trigger than any kit includes, and the upper is the part that actually matters for accuracy and reliability.
Essential accessories to round out your setup
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