AR-15 Buffer System Specifications
Buffer weights, springs, and tube dimensions for AR-15 carbine, mid-length, and rifle configurations. Includes an interactive calculator that recommends a starting buffer weight for your build.
Buffer Weights
| Buffer | Weight | Internal weights | Use case |
|---|---|---|---|
| Carbine | 3.0 oz | Three steel weights | Standard carbine gas, mid-length, most 16 in builds. |
| H (Heavy) | 3.8 oz | One tungsten, two steel | Mil-spec M4 (14.5 in carbine gas), most M4-pattern builds. |
| H2 | 4.6 to 4.7 oz | Two tungsten, one steel | Short carbine gas (11.5 in and under), suppressed M4. |
| H3 | 5.4 to 5.6 oz | Three tungsten | Pistol gas, heavily suppressed, short-barrel overgassed builds. |
| HSS (Heavy Sprinco) | 5.0 oz | Hybrid, brand dependent | Aftermarket option between H2 and H3. |
| Rifle | 5.0 to 5.4 oz | Longer, different diameter | A2 rifle stock only. Not interchangeable with carbine tubes. |
Source: Colt M4 TDP buffer assembly callouts and published buffer weights from Colt, BCM, KAC, and Spikes Tactical.
Springs
| Spring | Coils | Length | Use |
|---|---|---|---|
| Carbine spring | 37 to 39 coils | 10.0 to 10.6 in free length | Standard carbine buffer tube. |
| Rifle spring | 41 to 43 coils | 12.75 in free length | Rifle-length buffer tube only. |
| A5 / VLTOR (intermediate) | Intermediate length | Fits carbine tube with A5 buffer | Smooths out overgassed carbine builds while keeping carbine stock compatibility. |
| Sprinco Red / White / Blue / Green | Enhanced chrome silicon | Carbine length | Higher quality spring with tuned rates. Color indicates target application. |
Buffer Tube Dimensions
| Type | Outside diameter | Receiver thread | Rear face | Compatibility |
|---|---|---|---|---|
| Mil-spec | 1.148 in | 1.185-16 UN-2A | Flat rear face | Accepts mil-spec stocks. Thicker wall, forged or extruded 7075. |
| Commercial | 1.168 in (approx 0.020 in larger) | 1.170-16 UN-2A (slightly larger) | Angled rear face | Commercial stocks only. Not interchangeable with mil-spec stocks. |
| A5 | 1.148 in (mil-spec OD) | 1.185-16 UN-2A | Mil-spec | Accepts mil-spec stocks. Uses A5 buffer and intermediate spring. |
Source: Colt M4 TDP lower receiver thread callout, and Magpul / B5 Systems published stock compatibility notes. Commercial tubes are a legacy workaround from a short period when mil-spec tube extrusions were in short supply; they are considered inferior.
Buffer Weight Calculator
Enter your barrel length, gas system, and suppressor status for a starting buffer recommendation. Always verify with real-world function testing.
Recommended buffer
3.8 oz
Mil-spec M4 configuration is 14.5 in carbine gas with an H buffer. This is the baseline for that setup.
Calculator output is a starting point, not a guarantee. Confirm reliable lock-back on an empty magazine and no short stroking under your actual ammunition.
Disclaimer: Specifications are sourced from published military technical data packages, SAAMI standards, and manufacturer data sheets. Always verify critical dimensions with calibrated measuring tools.