Technical Reference

AR-15 Mil-Spec Standards: Complete Reference

Specifications for every major AR-15 component, pulled from published military technical data packages, SAAMI standards, and manufacturer material sheets. If a number is on this site, its source is cited beside it.

What "Mil-Spec" Actually Means

Mil-spec is shorthand for conformance to the military Technical Data Package (TDP) for the M16 and M4 family of rifles. The TDP is a bundle of drawings, material callouts, process specs, and inspection criteria maintained by the US Army. It does not describe a single rifle. It describes the minimum acceptance criteria a part must meet to be supplied to the military for service use.

Commercial AR-15 parts range from exceeding the TDP (target match barrels, tighter tolerance billet receivers) to failing it outright (cast receivers, untested bolts, understaked gas keys). "Mil-spec" alone is neither a floor nor a ceiling on quality. It is a specific document set, and a part either meets the callouts or it does not.

Key mil-spec documents referenced throughout this guide:

MIL-B-11595E: Steel, Chrome-Molybdenum-Vanadium for Gun Barrels
MIL-A-8625 Type III: Anodic Coatings for Aluminum, hard anodize class
MIL-DTL-16232: Phosphate Coatings, Heavy, Manganese or Zinc Base
MIL-STD-1916: DoD Preferred Methods for Acceptance of Product
TDP drawings: M16A2 / M4 Carbine Technical Data Package (dimensional callouts for bolt, carrier, barrel extension, receivers)

Spec Categories

Receivers

Forged vs billet, 7075-T6 vs 6061-T6 aluminum, MIL-A-8625 Type III hard anodize, and mil-spec dimensional tolerances.

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Barrels

4150 CMV vs 4140 vs 416R stainless, MIL-B-11595E chrome lining, twist rate by bullet weight, 5.56 NATO vs .223 Wylde chambers.

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Bolt Carrier Groups

Carpenter 158 vs 9310 steel, MPI and HPT testing, gas key staking, coating hardness and salt spray performance.

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Finishes and Coatings

Phosphate, nitride, nickel boron, DLC, TiN, chrome, Cerakote, and hard anodize compared on hardness, lubricity, and corrosion resistance.

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Buffer Systems

Carbine, H, H2, H3, and rifle buffer weights. Mil-spec (1.148 in) vs commercial (1.168 in) tube dimensions. Interactive weight calculator.

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Quick Reference Table

Common parts, the spec that matters, and the mil-spec value.

Part	Spec	Mil-spec value	Why it matters
Lower receiver	Aluminum grade	7075-T6 forged	Highest strength-to-weight of common aluminum alloys.
Lower receiver	Anodize	MIL-A-8625 Type III Class 2	Hard coat anodize, 50 to 75 Rockwell C, corrosion and wear resistant.
Barrel	Steel	MIL-B-11595E (4150 CMV)	Chrome-moly-vanadium handles sustained fire better than 4140.
Barrel	Chamber	5.56x45mm NATO	Longer leade handles both 5.56 NATO and .223 Rem safely.
Barrel	Chrome lining	0.002 in min bore and chamber	Per MIL-B-11595E, extends service life and eases cleaning.
Bolt	Steel	Carpenter 158	Called out by the military TDP for toughness and fatigue life.
Bolt	Testing	MPI and HPT	High pressure proof then magnetic particle inspection for cracks.
Carrier	Gas key	Grade 8 screws, properly staked	Staking prevents screws backing out under cyclic load.
Buffer tube	OD	1.148 in (mil-spec)	Commercial 1.168 in stocks will not fit mil-spec tubes.
Trigger pins	Diameter	0.154 in	Mil-spec lowers use small pin; large-pin Colt lowers use 0.170 in.

Disclaimer: Specifications are sourced from published military technical data packages, SAAMI standards, and manufacturer data sheets. Always verify critical dimensions with calibrated measuring tools. This reference is educational and not a substitute for a qualified gunsmith.

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