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300 Blackout Guide 2026: Barrel Length, Suppressors & Subsonic vs Supersonic Compared

The .300 AAC Blackout exists for one reason: to be the ultimate suppressed AR-15 cartridge. Designed from the ground up for short barrels and silencers, it delivers what 5.56 cannot: truly quiet subsonic capability with genuine terminal performance. This guide covers everything you need to build the perfect .300 BLK setup, from ammunition selection to suppressor pairing.

By AB|Last reviewed January 2026

Optimal Barrel

9"

The sweet spot. Complete powder burn, optimal suppressor performance, compact package. This is what .300 BLK was designed for.

Best Suppressor Pick

Q Trash Panda

Purpose-built for .300 BLK. Excellent suppression, reasonable weight, quick-attach mount. The OG choice for dedicated hosts.

Best Subsonic Load

Hornady 190gr Sub-X

Flex Tip designed for reliable expansion at subsonic velocities. The best factory option for terminal performance.

Why .300 Blackout Exists

The Problem: 5.56 NATO was designed for 20" barrels. Short barrels lose significant velocity, and the supersonic crack makes true suppression impossible.

The Solution: AAC developed .300 Blackout to deliver .30 caliber performance from short barrels while enabling genuine subsonic capability. Same bolt, same magazines, just swap the barrel. AAC is back with the MPW Series suppressor-optimized rifles in .300 BLK.

The Result: A cartridge that achieves complete powder burn in 9" barrels, works flawlessly with suppressors, and fires subsonic rounds that are genuinely hearing-safe.

Key Advantages
  • ✓ Same bolt & magazines as 5.56: barrel-only conversion
  • ✓ Optimal performance from 8-10" barrels
  • ✓ Subsonic loads are truly hearing-safe when suppressed
  • ✓ .30 cal bullets punch through barriers 5.56 cannot
  • ✓ Heavier subsonic bullets maintain lethality without velocity

Interactive .300 Blackout Builder

Compare loads, find optimal barrel lengths, and match suppressors.

Supersonic

FAST & LOUD
Velocity
2000-2400 fps
Energy
1000-1400 ft-lbs
Bullet Weights
110-150 grains
Effective Range
200+ yards
Best For
HuntingTrainingGeneral defensive use
Sonic crack cannot be suppressed
Still benefits from suppressor (reduced blast)
Superior energy and range
More ammunition options available

Subsonic

QUIET & HEAVY
Velocity
1000-1050 fps
Energy
450-500 ft-lbs
Bullet Weights
190-220 grains
Effective Range
75-100 yards
Best For
Suppressed useStealth applicationsUrban defense
Limited energy requires shot placement
Must use expanding ammo for defense
Heavy bullets = more recoil than 5.56
Rainbow trajectory past 100 yards

Velocity by Barrel Length

5.5"Super: 1850 fps | Sub: 1000 fps
7.5"Super: 2000 fps | Sub: 1010 fps
8.3"Super: 2075 fps | Sub: 1015 fps
9"Super: 2125 fps | Sub: 1020 fps
10.3"Super: 2200 fps | Sub: 1030 fps
12.5"Super: 2275 fps | Sub: 1040 fps
16"Super: 2375 fps | Sub: 1050 fps
Supersonic (110gr)
Subsonic (220gr)

Subsonic vs Supersonic: The Core Decision

This is THE decision that shapes your entire .300 BLK setup. Understanding the tradeoffs determines whether .300 BLK makes sense for you.

The Critical Understanding

Supersonic .300 BLK is ballistically INFERIOR to 5.56. Read that again. If you're running supersonic loads without a suppressor, you're paying 2-3x per round for worse external ballistics than 5.56.

There are only TWO reasons to choose .300 BLK over 5.56: (1) You want subsonic capability with a suppressor, or (2) you need a very short barrel (under 10") for a PDW setup, where 5.56 loses most of its velocity advantage and .300 BLK's ballistics degrade far less. Outside those scenarios, stick with 5.56.

Supersonic Loads (110-150gr)

When you need maximum terminal performance or extended range. Still loud even suppressed (sonic crack persists), but suppressor reduces blast significantly.

Ammunition

Ammunition • Mid-Range

Hornady V-MAX 300 Blackout 110gr

  • 110 grain V-MAX
  • 300 Blackout
$29.99
Check Price at OpticsPlanet
Ammunition • Budget

300 Blackout Training FMJ 125gr

  • 125 grain FMJ
  • 300 Blackout
Check Price at OpticsPlanet
Ammunition • Mid-Range

Barnes VOR-TX 110gr TAC-TX

  • 110 grain all-copper
  • .300 Blackout
$41.09
Check Price at OpticsPlanet
Ammunition • Premium

SIG Sauer 120gr Elite Copper Duty

  • 120 grain solid copper
  • .300 Blackout
$34.99
Check Price at OpticsPlanet
Ammunition • Mid-Range

Hornady Custom 125gr SST

  • 125 grain SST polymer tip
  • .300 Blackout
$37.99
Check Price at OpticsPlanet

Subsonic Loads (190-220gr)

The reason .300 BLK exists. Heavy bullets traveling below the speed of sound (~1,100 fps) eliminate the sonic crack, making suppressed fire genuinely quiet.

Ammunition

Ammunition • Mid-Range

Hornady V-MAX 300 Blackout 110gr

  • 110 grain V-MAX
  • 300 Blackout
$29.99
Check Price at OpticsPlanet
Ammunition • Budget

300 Blackout Training FMJ 125gr

  • 125 grain FMJ
  • 300 Blackout
Check Price at OpticsPlanet
Ammunition • Premium

Gorilla Ammunition 205gr Subsonic

  • 205 grain solid copper
  • .300 Blackout
Check Price at OpticsPlanet
Ammunition • Budget

Federal American Eagle 220gr OTM Subsonic

  • 220 grain OTM
  • .300 Blackout
Check Price at OpticsPlanet
Ammunition • Mid-Range

Hornady A-MAX 208gr Subsonic

  • 208 grain A-MAX
  • .300 Blackout
$33.99
Check Price at OpticsPlanet

.300 Blackout Barrel Length: Finding the Sweet Spot

Unlike 5.56, .300 BLK was designed for short barrels. Here's exactly where each length shines.

The Sweet Spot: 9"

Why 9"?

Complete powder burn for most loads. Optimal suppressor performance. Compact enough for vehicle/CQB use.

Performance

~2,125 fps supersonic (110gr), ~1,020 fps subsonic (220gr). Within 5% of maximum velocity.

Best For

Suppressed builds, home defense, PDW, duty use. The default recommendation.

LengthOAL SuppressedSuper Vel.Sub Vel.PowderBest For
5.5"28.5"1850 fps1000 fpsincompletePDW, vehicle gun
7.5"30.5"2000 fps1010 fpsincompletePDW, suppressor host
8.3"31.3"2075 fps1015 fpsincompletePDW, suppressor host
9"32"2125 fps1020 fpsoptimalsuppressor host, home defense
10.3"33.3"2200 fps1030 fpsoptimalsuppressor host, duty
12.5"35.5"2275 fps1040 fpscompleteduty, hunting
16"39"2375 fps1050 fpscompleterifle, hunting

Ultra-Short (5.5-7.5")

Maximum concealability for PDW/vehicle gun use. Expect incomplete powder burn with supers (more flash, less velocity). Subs remain fully effective. Requires careful gas tuning for reliability.

Standard (16")

Maximum velocity but defeats the purpose of .300 BLK. Only choose if you can't/won't SBR or use a pistol brace. At this point, consider if 5.56 makes more sense for your use case.

Best .300 Blackout Barrels

9 inches is the sweet spot for .300 BLK: complete powder burn, optimal suppressor performance, compact package. Here are our top barrel picks across price tiers.

9" · Gunner Profile · Nitride

Faxon 9" .300 Blackout Gunner Barrel

1
Best overall value
  • Optimal 9" sweet spot length
  • Gunner profile balances weight and rigidity
Check Price at OpticsPlanet
8.5" · CORE Profile · Chrome-lined

Criterion 8.5" .300 Blackout CORE Barrel

2
Best accuracy for the money
  • Hand-lapped chrome-lined bore
  • Sub-MOA accuracy with match ammo
$313.49
Check Price at OpticsPlanet
9" · Bloodline Series · Melonite

Rosco Bloodline 9" .300 Blackout Barrel

3
Best suppressed out-of-box
  • Excellent gas port sizing out of the box
  • Runs suppressed without AGB for many users
Check Price at OpticsPlanet
8.5" · Stainless Match-grade

Noveske 8.5" .300 Blackout Stainless Barrel

4
Best premium precision
  • 416R stainless for maximum precision
  • Hand-lapped match bore
Check Price at OpticsPlanet
8.5" · Modern Series · Nitride

Ballistic Advantage 8.5" .300 Blackout Barrel

5
Best budget option
  • Sub-MOA accuracy guarantee
  • Best budget entry point
Check Price at OpticsPlanet
7.5" · Gunner Profile · PDW

Faxon 7.5" .300 Blackout Gunner Barrel

6
Best ultra-compact PDW
  • Maximum concealability for PDW builds
  • Best paired with subsonic + suppressor
$140.60
Check Price at OpticsPlanet

Purchasing through these links may generate a commission at no extra cost to you.

The Gas Tuning Dilemma: .300 BLK's Dirty Secret

Here's what nobody talks about: you can't tune a gas system to run both supersonic and subsonic loads optimally. This is THE fundamental challenge of .300 Blackout.

The Core Problem

Subsonic loads produce ~60% less gas pressure than supersonic loads. A gas system tuned to reliably cycle 220gr subs will be massively over-gassed when you switch to 110gr supers.

The result: When running supers on a sub-tuned gun, the bolt carrier slams back violently, beating the rifle to death, causing excessive wear, and creating punishing felt recoil. Conversely, tune for supers and your subs may short-stroke or fail to lock back.

Add a suppressor and it gets worse. The added back pressure makes an already over-gassed super even more violent. Remove the suppressor and your sub-tuned gun might not cycle at all.

Solution 1: Adjustable Gas Block

The most common approach. Dial down gas for supers, dial up for subs.

Pros
  • • Allows optimization for any load
  • • Can compensate for suppressor on/off
  • • Many quality options (Superlative Arms, SLR, Wojtek)
Cons
  • • Must manually adjust when switching ammo types
  • • Tiny set screw can work loose or drift
  • • Reliability concerns under carbon buildup
  • • Adds complexity to a defensive weapon

Reality: Most people set it for subs and never touch it, accepting harsh super cycling.

Solution 2: Heavy Buffer + Spring

Increase buffer weight (H2/H3) and use a heavier spring to slow bolt carrier velocity.

Pros
  • • No moving parts or adjustments needed
  • • Set-and-forget reliability
  • • Works with most loads and suppressor configs
Cons
  • • Compromise, still over-gassed with supers
  • • May short-stroke with some subs unsuppressed
  • • Doesn't eliminate the problem, just masks it

Reality: Better than nothing, but you're still living with a compromise.

The Best Solution: SIG Rattler (Piston System)

The SIG MCX Rattler's piston system includes a two-position gas regulator that can be switched between "suppressed" (subs) and "unsuppressed" (supers) with a simple lever. No tiny screws, no tools, no counting clicks.

Why piston wins here: The gas system is self-contained in the handguard, isolated from the BCG. This makes gas adjustment more accessible and less prone to carbon fouling affecting the setting.

Rattler Specifics
  • • 5.5" barrel, ultra compact
  • • Quick-change barrel system
  • • Side-folding stock
  • • Purpose-built for .300 BLK role

Caveat: Still recoils pretty hard with supers. The physics of a 5.5" barrel and light platform don't change. But it's the cleanest solution to the tuning problem.

Practical Approach: Pick Your Lane

Subsonic-Primary Build

Tune for subs suppressed. Accept that supers will cycle hard. Use H2/H3 buffer to soften the blow. This is what most suppressed .300 BLK builds end up being.

Supersonic-Primary Build

Tune for supers. Use adjustable gas block and accept that subs may not cycle without the suppressor. Best if you rarely shoot subs or always shoot suppressed.

True Versatility

Buy a SIG Rattler/MCX or accept that you'll need to adjust your gas block when switching. There's no free lunch with DI guns on this caliber.

Best .300 Blackout Suppressors: Pairing Guide

.300 BLK was designed for suppression. Here are the top picks for different priorities.

Dedicated .300 BLK · Cherry Bomb QD

Q Trash Panda

1
Best dedicated .300 BLK can
  • Purpose-built for .300 Blackout
  • Compact for its performance
Shop at Primary Arms
Max suppression · Cherry Bomb QD

Q Thunder Chicken

2
Maximum suppression
  • Hollywood quiet with subs
  • Extended baffle stack for max suppression
Shop at Primary Arms
Multi-host · KeyMo / HUB / Direct

Dead Air Nomad 30

3
Best multi-host versatility
  • Industry-standard KeyMo mounting
  • Works great on .300 BLK and .308
Shop at Primary Arms
Ultra-quiet · Low back pressure

CGS Hyperion

4
Absolute maximum quiet
  • Among the quietest .30 cal cans made
  • No first-round pop
Shop at Primary Arms
Multi-caliber · ASR / KeyMo

SilencerCo Omega 300

5
Best lightweight multi-cal
  • Lightweight titanium construction
  • Proven track record across calibers
Shop at Primary Arms
Low back pressure · FLOW-LOK QD

HUXWRX FLOW 762 Ti

6
Best for gassy AR setups
  • Lightest .30 cal option at 11.4 oz
  • Reduces gas to shooter significantly
$138.00
Shop at Primary Arms

Purchasing through these links may generate a commission at no extra cost to you. Suppressors are NFA items requiring a $200 tax stamp and ATF Form 4 approval.

Suppressor Selection Factors

Back Pressure

Low back pressure = less gas in your face, less bolt speed increase. Important for AR platforms. HUXWRX FLOW leads here.

Mounting System

Dead Air KeyMo is the industry standard for QD. Q Cherry Bomb is great but proprietary. Direct thread is lightest but slowest to attach.

Sound vs Size

Longer suppressors = quieter but heavier and less maneuverable. CGS Hyperion is quietest; Q Trash Panda is most balanced.

.300 Blackout Cost: True Cost of Ownership

.300 BLK isn't cheap. Here's what you're actually signing up for.

The Ammo Reality Check

Supersonic: $0.50-$1.60/round (vs $0.35 for 5.56)

Subsonic: $0.85-$2.25/round

Reality: Training with .300 BLK costs ~1.5-2x what 5.56 does, down from 2-3x a few years ago.

Annual cost (1500 rounds): ~$1,020 vs $525 for 5.56

Difference: ~$500/year in ammo alone

Good news: Prices have stabilized significantly since the 2020-2023 spike.

Occasional range trips, 2-3 per year
$340
500 rounds/year
300 super + 200 sub
Monthly range visits, 100 rounds average
$1,020
1,500 rounds/year
900 super + 600 sub
Weekly shooter, training focus
$2,040
3,000 rounds/year
1800 super + 1200 sub
Handloading from converted 5.56 brass
$770
2,000 rounds/year
1000 super + 1000 sub

Build Cost Breakdown

ItemBudgetMid-RangePremiumNotes
Complete .300 BLK Upper$350$650$1200PSA budget, BCM/Aero mid, DD/LWRC high-end
Barrel Only (9" .300 BLK)$125$225$400BCA budget, Ballistic Advantage mid, Criterion high-end
Dedicated .30 Cal Silencer$400$800$1400Form 1 DIY, Trash Panda mid, CGS Hyperion high-end
Tax Stamp$200$200$200Required $200 NFA tax for suppressor or SBR
Tax Stamp (if SBR)$200$200$200Required if barrel under 16" and using rifle stock
Supersonic (per 20 rounds)$10$16$32Training FMJ to premium hunting ammo
Subsonic (per 20 rounds)$17$24$45Budget plinking to premium defensive subs

Reloading: The Cost Saver

Reloading .300 BLK drops cost to ~$0.35/round supersonic, ~$0.42/round subsonic using converted 5.56 brass. Initial equipment investment ($400-800) pays for itself within 1,500-2,000 rounds. For serious .300 BLK shooters, reloading is almost mandatory.

Critical Safety: .300 BLK and 5.56 Magazine Mix-Ups

A .300 Blackout round WILL chamber in a 5.56 barrel. When fired, the .308 bullet cannot exit the .224 bore. The result is catastrophic failure: destroyed rifle, potential severe injury or death.

This happens because both cartridges use the same parent case (.223 Remington). Standard AR-15 magazines feed both calibers without modification.

Prevention (Non-Negotiable):

  • • Color-code ALL .300 BLK magazines (use distinct color like FDE or tan)
  • • Mark/engrave all .300 BLK uppers prominently
  • • NEVER store mixed ammunition together
  • • Use dedicated range bag for .300 BLK equipment
  • • Verify caliber before EVERY loading session

Hunting with .300 Blackout

Supersonic Hunting (Recommended)

  • Barnes 110gr TAC-TX: The gold standard. Devastating on hogs and deer.
  • Effective range: 150-200 yards with proper bullet selection
  • Game: Whitetail, hogs, coyotes, excellent. Larger game not recommended.

Subsonic Hunting (Specialized)

  • Hornady 190gr Sub-X: Only factory sub designed for expansion
  • Effective range: 50-75 yards maximum
  • Game: Hogs only. Energy similar to .45 ACP, so shot placement is critical.

For deer hunting beyond 150 yards, consider 6.5 Grendel. .300 BLK trades range for suppression capability.

Should You Build in .300 Blackout?

Build .300 BLK If:

  • ✓ You own or will buy a suppressor
  • ✓ You want genuine quiet capability (subs)
  • ✓ You need a compact SBR/PDW platform
  • ✓ You can afford 2-3x ammo costs
  • ✓ You want .30 cal barrier performance

Stick with 5.56 If:

  • ✗ You don't own/plan to own a suppressor
  • ✗ Budget constraints on ammo
  • ✗ This would be your only AR
  • ✗ You need range beyond 200 yards
  • ✗ You value cost-effective training

The honest answer: .300 BLK is a fantastic cartridge for its intended purpose: suppressed SBR use. Outside that niche, 5.56 does almost everything better for less money. Build .300 BLK as a dedicated suppressor host, not as a general-purpose rifle.

Further Learning: Brass Facts

For in-depth analysis and testing, we recommend Brass Facts on YouTube, one of the best resources for honest, data-driven .300 Blackout content.

External links open in new tab. We're not affiliated with Brass Facts, just fans of quality content.

Magazines

Magpul PMAG 30 .300 BLK

  • Distinct pattern for quick caliber ID
  • Same reliability as standard PMAGs
$43.75
Check Price at OpticsPlanet
Magazines · Visual ID

Lancer L5AWM .300 BLK Smoke

  • See-through body for round count
  • Steel feed lips for durability
$27.49
Check Price at OpticsPlanet
Gas Tuning · Tool-Free

Riflespeed Adjustable Gas Block

  • Tool-free click adjustment at the range
  • 24 positions for precise sub/super tuning
Check Price at OpticsPlanet
Gas Tuning · Bleed-Off

Superlative Arms Adjustable Gas Block

  • Bleed-off design reduces gas to shooter
  • Tool-less adjustment with detents
Check Price at OpticsPlanet
Buffer Tuning

H2/H3 Buffer Weight

  • Tungsten weights for compact mass
  • H2 for most, H3 for SBRs
Check Price at OpticsPlanet

Purchasing through these links may generate a commission at no extra cost to you.

Frequently Asked Questions

Is 300 Blackout good for home defense?
Yes, especially suppressed with subsonic loads. The 9" barrel is optimal for home defense builds, offering complete powder burn and hearing-safe operation when suppressed.
What is the best barrel length for 300 Blackout?
9 inches is the sweet spot. It provides complete powder burn, optimal suppressor performance, and compact size for PDW/home defense use.
Is 300 Blackout better than 5.56?
Only if you plan to use a suppressor. Supersonic 300 BLK is ballistically inferior to 5.56. The only reason to choose 300 BLK is subsonic capability with a suppressor.
How much does 300 Blackout ammo cost?
Supersonic: $0.50-$1.60/round. Subsonic: $0.85-$2.25/round. Annual cost for 1500 rounds is approximately $1,020 vs $525 for 5.56.
Can I use 5.56 magazines for 300 Blackout?
Yes, standard AR-15 magazines work with both calibers. However, you must color-code and mark all 300 BLK magazines to prevent dangerous mix-ups, as a 300 BLK round will chamber in a 5.56 barrel with catastrophic results.
Is 10.5 inches too long for 300 Blackout?
No, 10.5 inches is not too long - it's a solid choice that offers complete powder burn for both supersonic and subsonic loads. However, 300 Blackout was designed for short barrels and achieves full powder burn around 9 inches. Going longer than 10.5 inches provides minimal velocity gains (maybe 50 fps) while adding length and weight. Most 300 BLK builds run 8-10 inches to maximize the caliber's compact advantage.
Is a 7 inch barrel good for 300 Blackout?
A 7 inch barrel works for 300 Blackout but isn't optimal. You'll lose about 100-150 fps compared to a 9 inch barrel, and some supersonic loads may not fully stabilize. For suppressed subsonic use at close range (home defense, CQB), 7 inches is acceptable. For general purpose use with both supersonic and subsonic ammo, 8-9 inches is the sweet spot. Below 7 inches, reliability and ballistics suffer significantly.