.300 Blackout Barrel Length vs Velocity

By Cole Harlan, Editor·Data checked Nov 4, 2026·How we verify·Editorial standards·Corrections

.300 Blackout velocity by barrel length

Velocity at every published length

Muzzle velocity in feet per second. Longest barrel first. A dash means not tested/published at this length.

Velocity lost per inch

This is how many fps each load loses for every inch cut off, between two lengths. Figures marked “calculated by GunReleases” are (fast velocity − slow velocity) ÷ (long length − short length) from the published points, to 1 decimal. “Tester’s stated avg” figures are the tester’s own.

Best barrel length for .300 Blackout: the trade-offs

We don’t pick one length. Here is what the test measured in each common range, and what each choice costs.

• Under 16 in (SBR or suppressed build; NFA rules apply). At 7.5 in the loads measured 989 to 2055 fps. At 10.5 in the loads measured 1048 to 2229 fps.
• About 16 in (shortest non-NFA rifle length; 16.5 in is the published length). At 16.5 in the loads measured 1082 to 2376 fps.

• Handling: a longer barrel adds length and weight out front; a shorter one is easier to carry and swing.
• Suppressors: a suppressor adds length and weight at the muzzle, so a shorter barrel with a suppressor can end up about as long overall as a longer bare barrel. We have no velocity data with a suppressor mounted, so none is shown.

Subsonic loads behave differently from supersonic ones. Lucky Gunner reports that two subsonic loads, Magtech 200 gr FMJ and Hornady 190 gr Sub-X, went past the speed of sound from the 16.5 in barrel (it cites roughly 1100 to 1125 fps). Its numbers for those two at 16.5 in were 1139 and 1107 fps. Lucky Gunner also states that its supersonic loads gained an average of 238 fps (13%) from 7.5 in to 16.5 in; the chart shows 4 of its supersonic loads.

Box velocity vs measured

Hornady lists 2375 fps for its 110 gr V-MAX BLACK load from a 16 in test barrel. Lucky Gunner tested Hornady’s 110 gr V-Max load and measured 2376 fps from its 16.5 in barrel.

SAAMI’s Z299.4 (centerfire rifle) sets the test barrel for .300 Blackout at 16 in for rifle ballistics, measured muzzle to breech face. SAAMI lists .300 AAC Blackout as an exception to its 24 in rule, at 16 in.

Federal minimum barrel length

Under 27 CFR 478.11, “Short-barreled rifle. A rifle having one or more barrels less than 16 inches in length…” A short-barreled shotgun is one with barrels “less than 18 inches in length.” Those are NFA firearms. Read the rule at eCFR 27 CFR 478.11, and see our SBR rules for 2026, the state NFA checker and the suppressor buying guide. Tester barrels shorter than 16 in on this page show what velocity does, not what you may build. This is not legal advice; state law can add limits.

How this was measured

• Test setup. Three different factory barrels (7.5 in DPMS 1:7, 10.5 in PSA 1:7, 16.5 in SIG 1:6), not one barrel cut down; Garmin Xero C1 Pro chronograph; 5-shot averages.
• Our part. We copied each published number exactly. We did not average, smooth, estimate or fill in any length. A dash means the tester did not publish that length. The underlying measurements belong to the testers credited above; our compilation is CC BY 4.0.
• Limits. This is one test series with one rifle or pistol frame, one chronograph and one day’s weather. Your results will differ.
• Different barrels. Lucky Gunner used three factory barrels, not one barrel cut down. Differences between lengths here include barrel-to-barrel variation. We show 7 of its 13 loads.

Download the data

barrel-length-velocity-300-blackout.csv has every number on this page with its source and test conditions. The combined file for all calibers and the barrel length vs velocity hub have the rest. Free to reuse under CC BY 4.0.

Frequently asked questions

Related

• Barrel length vs velocity: all calibers
• 9mm Luger barrel length vs velocity
• .380 ACP barrel length vs velocity
• .40 S&W barrel length vs velocity
• .357 SIG barrel length vs velocity
• .45 ACP barrel length vs velocity
• 10mm Auto barrel length vs velocity
• .38 Special barrel length vs velocity
• .357 Magnum barrel length vs velocity
• .44 Magnum barrel length vs velocity
• .45 Colt barrel length vs velocity
• .22 LR barrel length vs velocity
• .22 WMR (.22 Magnum) barrel length vs velocity
• 5.56 NATO / .223 Rem (AR-15) barrel length vs velocity
• .224 Valkyrie barrel length vs velocity
• 7.62x39 barrel length vs velocity
• .308 Win / 7.62 NATO barrel length vs velocity
• 6.5 Creedmoor barrel length vs velocity
• .243 Winchester barrel length vs velocity
• 7mm Remington Magnum barrel length vs velocity
• .300 Winchester Magnum barrel length vs velocity
• New ammo for 2026
• Pistol brace rule 2026
• New AR-15s 2026
• All GunReleases data

Sources

1. Lucky Gunner Lounge: .300 Blackout ballistics
2. SAAMI Z299.4 (centerfire rifle)
3. eCFR: 27 CFR 478.11, definitions (short-barreled rifle)
4. Hornady: .300 Blackout 110 gr V-MAX BLACK

Supplementary sources

News reports, advocacy groups, dealer practice and unofficial copies. They add context or report statements; the primary sources above control.

1. Cornell LII: 26 U.S.C. 5845, NFA definitions