How we chose
IronScout doesn't sell ammo and doesn't earn affiliate commissions. Our picks are based on:
- Noise reduction — metered decibel levels when suppressed, aiming for hearing-safe or near hearing-safe
- Cycling reliability — consistent function in gas-operated AR-15 platforms, both direct impingement and piston
- Accuracy — acceptable precision (2 MOA or better) at subsonic velocities
- Availability — regularly stocked, not specialty runs that sell out in hours
- Suppressor compatibility — no baffle strikes, safe for standard .30 caliber silencers
We're not picking a single "best" because your suppressor, gas system setup, and use case all matter.
Top picks by category
Budget — Magtech 200gr FMJ Subsonic
Magtech's 200gr subsonic is the workhorse of the .300 BLK suppressed shooting world. It's loaded specifically for reliable cycling in AR-pattern rifles, runs consistently subsonic from 8"–16" barrels, and costs less than most competitors. The 200gr FMJ isn't expanding — this is a range and training load for suppressed shooting, not a defensive round.
Typical price: $0.65–0.90/rd
Why this might not be for you: FMJ means no expansion. This is a plinking and training load. For anything beyond target shooting, you need a bullet designed to expand at subsonic velocities. Also, Magtech occasionally produces batches that run right at the transonic boundary from 16" barrels — if you're running a 16" barrel, chrono a sample to confirm subsonic velocity.
Mid-tier — Hornady Sub-X 190gr
The Sub-X uses Hornady's flex-tip design specifically engineered to expand at subsonic velocities — a problem most JHP designs can't solve because they rely on hydraulic pressure that requires higher impact speeds. The 190gr weight offers a good balance between expansion potential and penetration depth. Hornady loads this to cycle reliably in standard gas systems.
Typical price: $1.00–1.40/rd
Why this might not be for you: Expansion at subsonic velocities is inherently limited. Even the Sub-X won't mushroom like a supersonic JHP — expect 0.45–0.55" expanded diameter versus 0.65–0.80" from a supersonic defensive load. If maximum terminal performance is your priority, supersonic .300 BLK (110–125gr) is significantly more effective, just louder.
Premium — Discreet Ballistics 188gr Selous Machined Expander
Discreet Ballistics builds .300 Blackout subsonic ammo exclusively — it's all they do. The Selous Machined Expander is a solid copper bullet CNC-machined with petals designed to open at subsonic velocities. It produces the most consistent subsonic expansion of any factory load currently available. Velocity spreads are tight, and the machined construction eliminates the jacket-separation risk of traditional JHP designs.
Typical price: $1.80–2.50/rd
Why this might not be for you: The price. At $2+/rd, you'll burn through money fast if you're also using this for range sessions. Buy Magtech 200gr FMJ for volume work and keep the Discreet Ballistics for your loaded magazines. Also, availability is spotty — Discreet Ballistics is a small operation that sells out quickly.
If your pick is out of stock
| If you can't find... | Try instead |
|---|---|
| Magtech 200gr FMJ | Sellier & Bellot 200gr FMJ Subsonic or Remington 220gr OTM |
| Hornady Sub-X 190gr | Sig Sauer 220gr OTM Subsonic or Federal American Eagle 220gr OTM |
| Discreet Ballistics 188gr | Lehigh Defense 194gr Maximum Expansion or Hornady Sub-X 190gr |
What to avoid
Supersonic .300 BLK through a suppressor expecting quiet. It'll work mechanically, but a 110gr supersonic .300 BLK through a suppressor still produces 130–140 dB from the sonic crack alone. If quiet is the goal, you need subsonic.
Reloaded / remanufactured subsonic ammo. Subsonic .300 BLK operates in a narrow velocity window — fast enough to cycle the action, slow enough to stay below 1,125 fps. Inconsistent loads can produce rounds that don't cycle or rounds that go supersonic and crack. Factory ammo from reputable manufacturers is worth the premium for reliability.
Standard JHP bullets loaded subsonic. Many JHP designs require 1,400+ fps to initiate expansion. A traditional 125gr JHP loaded to 1,050 fps will just pencil through like FMJ. Only buy subsonic ammo with bullets specifically designed for subsonic expansion (Sub-X, Selous, Lehigh Maximum Expansion).
Gas system notes
Subsonic .300 BLK produces significantly less gas pressure than supersonic. This affects cycling:
Adjustable gas block (recommended). Open the gas port for subsonic, restrict it for supersonic. This gives reliable cycling with both load types. If you're building a dedicated suppressed .300 BLK, an adjustable gas block is essentially mandatory.
Standard gas block. Most factory .300 BLK rifles with pistol-length gas systems will cycle 200gr+ subsonic ammo through a suppressor. The suppressor adds back-pressure that helps. Without a suppressor, many standard gas systems won't cycle subsonic reliably.
Buffer weight. A lighter buffer (carbine instead of H2) improves subsonic cycling. Some shooters run a standard carbine buffer for subsonic and swap to an H2 for supersonic. Adjustable buffers exist for quick changes.
Magazine spring. Weak magazine springs can cause feeding issues with heavy subsonic rounds. Quality magazines (Magpul PMAG, Lancer) in good condition are important.
What this costs
Suppressed .300 BLK is not a budget hobby. Between ammo cost, suppressor investment, and tax stamp, the total picture:
| Item | Cost |
|---|---|
| Subsonic ammo (1,000 rds/year) | $650–1,400 |
| Suppressor | $400–1,200 (one-time) |
| NFA tax stamp | $200 (one-time) |
| Adjustable gas block | $80–150 (one-time) |
Compare to 5.56 unsuppressed: 1,000 rounds of 5.56 FMJ costs $300–420. The quiet tax is real.
Compare current .300 BLK subsonic prices →
The terminal performance reality
Subsonic .300 BLK is quieter than almost any other centerfire suppressor combination. It's not as effective on target as supersonic rifle rounds. Both things are true simultaneously.
At ~1,050 fps, a 190–220gr subsonic .300 BLK bullet carries roughly the same energy as a .45 ACP +P — about 480–520 ft-lbs at the muzzle. That's adequate for close-range defense, but it's a fraction of what supersonic .300 BLK (110gr at 2,300 fps = ~1,290 ft-lbs) or 5.56 NATO (62gr at 3,100 fps = ~1,325 ft-lbs) delivers.
For home defense with a suppressed .300 BLK, many experienced shooters keep one magazine of subsonic and one of supersonic — subsonic for noise-critical scenarios, supersonic for maximum terminal effect. Your situation determines which you grab.
Read more: .300 Blackout vs 5.56 for home defense →
The bottom line
Magtech 200gr FMJ for affordable range work with your suppressor. Hornady Sub-X 190gr for the best balance of expansion and availability. Discreet Ballistics 188gr if you want the most effective subsonic terminal performance available and can stomach the price.
Whatever you choose, confirm cycling in your specific rifle/suppressor/buffer combination before relying on it. Subsonic .300 BLK is more sensitive to gas system tuning than any other common AR caliber.
Set a price alert for .300 BLK subsonic →
Related articles
Sources
- .300 AAC Blackout — Wikipedia — Subsonic design specifications
- Hornady Sub-X Technology — Subsonic expanding bullet design
- SAAMI .300 Blackout Specifications — Pressure and velocity standards