Balance dwell time, port sizing, and mass to keep AR-pattern rifles trustworthy. Use these tables to choose gas systems, buffer weights, and maintenance cycles that survive suppressors, seasonal ammo changes, and high round counts.
Dwell time is the barrel length from the gas port to the muzzle. Longer dwell increases impulse and lets the carrier travel further before uncorking. Use these windows to inform port sizing and mass.
| Barrel | Gas system | Dwell window | Notes |
|---|---|---|---|
| 10.3"–11.5" | Carbine | 3.8"–4.7" | Short dwell and high port pressure. Runs best with adjustable gas blocks and heavier buffers when suppressed. |
| 12.5"–13.7" | Carbine or Mid | 5.5"–6.5" | Sweet spot for hybrid duty builds. Carbine gas hits harder suppressed; mid-length softens recoil with quality ammo. |
| 14.5"–16" | Mid | 7.0"–7.8" | Most forgiving combination. Standard H or H2 buffer keeps cyclic rate steady unsuppressed and with low backpressure cans. |
| 18"–20" | Rifle | 8.5"–9.5" | Low port pressure. Needs lighter buffers or rifle-length action springs to maintain reliability in cold weather. |
Pair your barrel length and mission profile with buffers, springs, and gas adjustments that armorers lean on before changing hard parts.
Adjustable gas block one click past lock-back, H2 or H3 buffer, Sprinco Blue spring, vented charging handle.
Spare O-rings, H1 buffer, carbine spring for extreme cold, note card with gas block baseline setting.
Mid-length gas if possible, H2 buffer, Sprinco Blue spring, A5 buffer system if running full-time suppressed.
H buffer for low-pressure ammo, spare gas rings, note on muzzle device alignment for suppressor installs.
Rifle gas, standard rifle spring with A2 buffer or VLTOR A5H1, match ammo gas tune via adjustable block.
A5H2 buffer for suppressor work, spare adjustable block set screws, torque wrench for gas block service.
14.5" mid-length, H buffer, quality chrome-lined barrel, keep spare BCGs and action springs in rotation.
Armorers log, go/no-go gauges, castle nut wrench, gas key staking tool.
Start with symptom-driven diagnostics before swapping major parts. Logging fixes keeps fleet carbines consistent.
Record your final gas setting, buffer weight, and spring choice in the build log. The next time round count spikes or suppressor configs change, you'll have a baseline to return to instead of guessing.