Pick every part.
Compare every price.
Pick parts. Check compatibility. Compare prices across retailers. Save and share your build.
Lower Receiver
Aero M4E1 Stripped Lower
Upper Receiver
Aero M4E1 Assembled Upper
Barrel
Ballistic Adv. 16" Hanson
BCG
Toolcraft Nitride BCG
Handguard
Midwest Industries 15"
Parts
Complete Rifles
Retailers
State Legal Guides
Compatibility Engine
Real-time validation catches incompatible parts before you buy. Platform, caliber, gas system, and barrel nut checks on every part.
Price Comparison
Same part, multiple retailers. Find the best deal without opening a dozen browser tabs.
Save & Share
Save your build with a shareable link. Get feedback from friends or the community before pulling the trigger.
Browse by State
Click your state to see AR-15 laws, magazine limits, and compliance requirements.
Explore
Builder
Configure your AR-15 build
Budget Builder
Plan a build by price
Shop
Browse complete rifles
State Laws
50-state legal guide
Ballistics
Velocity, drop, energy tables
Specs
Mil-spec reference for every part
Gas System
Length, dwell, tuning calculator
Torque Specs
Every fastener, every value
Maintenance
Round count service schedule
Twist Calc
Optimal twist rate by bullet weight
Weight Calc
Estimate total rifle weight
Tools & Calculators
Plan, tune, and maintain your rifle with free interactive reference tools.
Gas System
Barrel length, dwell time, and buffer tuning
Weight Calculator
Target a build weight and find lighter parts
Maintenance Schedule
Round count based service checklist
Twist Rate Calculator
Find the right barrel twist for your bullet weight
Torque Reference
Every fastener torque spec and thread locker
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