5.56 vs 300 Blackout: cost per round and uses

Put a 300 Blackout cartridge next to a 5.56 and the family resemblance is obvious: same case head, about the same overall length, both made to run in an AR-15. Then you notice the bullet. 5.56 pushes a light .22-caliber bullet very fast. 300 Blackout puts a much heavier .30-caliber bullet on a shorter case, and it can be loaded either supersonic or subsonic. This guide covers where each cartridge came from, what changes between them, what each one is good at, why you must never mix them up, and what each costs to shoot.

The short answer

• 5.56 NATO is the standard AR-15 cartridge: a light, fast bullet with a flatter trajectory, and it has generally been the cheaper of the two to shoot. It's the usual pick for high-volume practice, training and longer-range shots. Browse 5.56 NATO.
• 300 Blackout (300 AAC Blackout, or 300 BLK) was designed by Advanced Armament Corp. (AAC) to fire .30-caliber bullets from an AR with only a barrel change. It shines in short barrels and with suppressors, especially with heavy subsonic loads. Browse 300 Blackout.
• Same bolt, same magazines, different barrel. That convenience is also the main hazard: a 300 Blackout round can chamber in a 5.56 rifle, and firing it can destroy the gun. Keep the two strictly separate.
• Cost: 5.56 practice ammo has generally cost less per round than 300 Blackout. That's a long-running pattern, not a guarantee. The tables below show cost per round for both.

5.56 vs 300 Blackout at a glance

Dimensions and pressures come from SAAMI's centerfire rifle standard. .223 Remington is the SAAMI commercial cartridge with the same outside dimensions as 5.56 NATO. 5.56 NATO is a military cartridge loaded to its own standard, and the two aren't fully interchangeable. See .223 vs 5.56 for which one your rifle can safely fire.

Where each cartridge came from

5.56 NATO and .223 Remington

5.56 is the incumbent. American Rifleman describes it as the "heavyweight" of intermediate cartridges, with a huge number of firearms chambered for it, decades of development and support from practically every major ammunition maker. It follows the small-caliber, high-velocity idea: a light bullet driven fast for low recoil and a flat trajectory. You'll see it sold as 5.56 NATO, 5.56x45mm and, in its commercial form, .223 Remington. Price Dope lists 5.56 NATO and .223 Remington separately, because they aren't fully interchangeable.

300 AAC Blackout

The idea of a .30-caliber bullet on a short, AR-compatible case is older than the name. Firearms News traces it to wildcats based on Remington's .221 Fireball case, including the .300/.221 Fireball and J.D. Jones' trademarked .300 Whisper, which were built to fire heavy subsonic bullets with a suppressor and lighter bullets at supersonic speed.

The standardized version came from AAC. According to Firearms News, a government customer asked whether AAC could supply .30-caliber AR rifles with Remington-made ammunition. AAC's research and development director, Robert Silvers, explains that Remington would only load SAAMI-standard cartridges, so AAC wrote final specifications and submitted them to SAAMI under a new name. SAAMI accepted the cartridge on January 17, 2011, as 300 AAC Blackout, with the short name 300 BLK, giving rifle and ammunition makers one common standard to build to. The design goals included reliable function in the AR platform, the best possible performance with suppressors, supersonic loads that match 7.62x39mm ballistics, and full use of existing M16 magazines.

What's shared and what isn't

Shared: SAAMI's drawings give 300 BLK the same rim and case-head dimensions as .223 Remington, which is why it uses a standard AR bolt. Both have the same 2.260-inch maximum cartridge length, which lets both fit standard AR magazines. AAC chose this route on purpose: a cartridge like 7.62x39mm needs a larger bolt face and its own magazines in an AR, while 300 BLK needs only a barrel.

Different: the 300 BLK case is much shorter (1.368 inches vs 1.760 inches for .223 Remington), and its neck is opened up to hold a .308-inch bullet instead of a .224-inch one. Everything else follows from that: much heavier bullets, lower velocities and a far wider range of bullet weights.

Magazines in practice: standard AR magazines work, and AAC designed the cartridge to use them at full capacity. Magpul makes a dedicated 300 BLK magazine because the wide range of 300 BLK bullet weights and shapes can affect reliability in magazines designed for 5.56, and because a magazine that looks and feels different helps prevent mix-ups.

Bullet weights and velocity

Here are published figures for named factory loads. Velocities are the manufacturers' numbers from their test barrels, and your rifle will give different results, especially with a shorter barrel. Hornady lists a 16-inch test barrel for both of its loads below. SAAMI's reference test barrel is 16 inches for 300 BLK and 24 inches for .223 Remington.

Two things stand out. First, supersonic 300 Blackout and 5.56 start with broadly similar muzzle energy in these examples, but they get there differently: 5.56 with a light bullet at high speed, 300 Blackout with a bullet two to three times heavier at lower speed. Second, the velocity gap shows up as drop. Federal publishes trajectories for a 100-yard zero with sights 1.5 inches above the bore. At 300 yards, its 55 gr 5.56 load is 12.1 inches low, its 150 gr 300 Blackout load is 34.7 inches low and its 220 gr subsonic load is 110.4 inches low.

That's why 5.56 is usually the better choice for longer shots, while 300 Blackout is at its best at shorter range.

Supersonic vs subsonic 300 Blackout

The speed of sound in dry air at 68°F is about 1,126 fps, according to Firearms News. American Rifleman notes it rises with temperature and drops at altitude. A bullet faster than that makes a sharp crack along its flight path. A subsonic bullet doesn't.

300 Blackout was designed to do both:

• Supersonic loads use lighter bullets. Firearms News puts typical 110- to 125-grain loads at roughly 2,350 to 2,250 fps, and AAC's goal was to match 7.62x39mm ballistics.
• Subsonic loads use heavy bullets, typically around 190 to 240 grains, kept below the speed of sound. Heavy .30-caliber bullets carry their velocity and energy well for their speed, which is what makes a subsonic rifle load practical.

A few practical points:

1. They hit in very different places. Federal's published drops above show how far apart a supersonic and a subsonic load land at the same zero. If you switch between them, confirm your zero or holds on paper for each load.
2. Your rifle may need tuning. AAC set out to make 300 Blackout run both kinds of ammunition without an adjustable gas system, and Firearms News says a well set-up AR can switch between them just by changing ammo. Tactical Life notes that in practice, a rifle set up for heavy subsonic rounds may not run as well with light supersonic ones, and switching sometimes takes a buffer or gas change. American Rifleman adds that subsonic ammo can cause feeding, extraction or ejection problems in gas-operated ARs, suppressed or not, and that a gas-block adjustment usually addresses it. Test both in your rifle.
3. 5.56 doesn't do subsonic well. Tactical Life points out that 5.56 relies on velocity and loses its advantages at subsonic speeds. If quiet subsonic rifle shooting is the goal, 300 Blackout was built for it.

Suppressor use

Subsonic 300 Blackout is the usual pick for quiet suppressed rifle shooting. Federal says its subsonic 300 Blackout load improves noise reduction through a suppressor and avoids the crack that supersonic loads make. Hornady says its subsonic loads lack the loud report of a supersonic round and are quieter still with a suppressor. American Rifleman notes that 5.56 can be difficult to suppress well while keeping its supersonic performance.

Supersonic ammunition can still be fired through a suppressor and is substantially quieter than unsuppressed, according to American Rifleman, but the bullet's crack remains. Federal's suppressor line also uses clean-burning powders to make cleanup easier, since it says conventional ammunition can cause heavy fouling in suppressed firearms.

Suppressors are regulated as firearms under the National Firearms Act (NFA), and some states and localities restrict or ban them. NFA requirements have changed over the years and can change again, so check ATF's current guidance and your state and local law before you buy, build or travel with one.

Short barrels

5.56 depends on speed. American Rifleman notes it can fare very poorly in shortened barrels for exactly that reason. 300 Blackout was designed to be efficient in short barrels. As one example from AAC's own data, AAC listed its 110-grain TAC-RRLP load at 2,400 fps from a 16-inch barrel and 2,190 fps from a 9-inch barrel. That's manufacturer data for one load, and results vary by rifle and ammunition.

Barrel length has legal consequences too. Under federal law, a rifle with a barrel shorter than 16 inches is regulated under the NFA as a short-barreled rifle, and state and local rules vary. Check federal, state and local law before you buy or build a short-barreled AR in either caliber.

Swapping an AR between 5.56 and 300 Blackout

This is 300 Blackout's big selling point. Firearms News and Shooting Illustrated both describe the conversion as a barrel change: the existing 5.56 bolt and magazines keep working, and the rest of the rifle stays the same. Follow the barrel or upper manufacturer's instructions, and have a qualified gunsmith do the work if you aren't sure.

Typical uses

5.56 NATO

• Practice, training and competition. A light-recoiling, widely made cartridge that's practical to shoot in volume.
• Varmints and predators. MeatEater calls it perhaps the best coyote cartridge on the market, thanks to its flat trajectory.
• Longer shots. Its trajectory gives it a clear edge over 300 Blackout as distances grow.
• Hunting larger game. MeatEater notes that many deer are taken with 5.56/.223 using loads designed for medium game, though some experts consider it light for that job. Check your state's hunting regulations for legal cartridges and bullets.

300 Blackout

• Suppressed shooting. Subsonic loads with a suppressor are what the cartridge is best known for.
• Short barrels. It was designed to keep its performance in compact rifles.
• Deer and hogs at shorter range. MeatEater's writer reports good results on deer and hogs within about 100 yards, and notes that most subsonic ammunition isn't designed for hunting. American Rifleman warns that many subsonic rifle loads use bullets that won't expand at subsonic speed, so if you hunt with subsonic 300 Blackout, pick a load built to expand at those velocities, such as Hornady's Sub-X. Check your state's hunting regulations.

What each costs to shoot

On cost, 5.56 has the edge. MeatEater found that 5.56 "pulls ahead when it comes to cartridge cost and availability," and Tactical Life lists lower ammunition cost among 5.56's advantages, describing 300 Blackout as generally available, though more expensive. That fits 5.56's position as the most widely supported AR cartridge. Treat it as a general pattern, not a rule: sales, supply swings and the specific load can change the picture, so check the tables below.

Compare like with like. FMJ practice ammo, subsonic suppressor ammo and expanding hunting or defensive loads are different products in both calibers, so filter by bullet type and weight on the caliber pages before you compare. More on how to compare boxes in cost per round, explained.

The tables show cost per round from the best price we have: MSRP for now, retailer prices as they join Price Dope.

To see where these sit among other popular calibers, see the cheapest calibers to shoot.

5.56 NATO cost per round

.223 Remington cost per round

Only buy .223 Remington and 5.56 for the same rifle if its barrel is marked for 5.56 NATO or .223 Wylde and the manufacturer approves both. Details in .223 vs 5.56.

300 Blackout cost per round

300 Blackout, 220 grain (a common subsonic weight)

220 grain is a common subsonic weight (it's the weight of Federal's subsonic load above), so this table is a quick way to look at subsonic options. Not every subsonic load is 220 grain, so check the listing's velocity before you buy.

Every listing, with filters for bullet weight, bullet type and case material, is on the 5.56 NATO, .223 Remington and 300 Blackout caliber pages.

Small gaps add up. A difference of 10 cents a round is $100 over 1,000 rounds. Plug in any listing:

How to choose

1. Start with the job. High-volume practice, training, longer shots or varmints point to 5.56. Suppressed shooting, short barrels or shorter-range hunting point to 300 Blackout.
2. Check what you already own. If you have a 5.56 AR, adding 300 Blackout takes a barrel or a complete upper. If you're shopping for a rifle, browse rifles in Buy Guns.
3. Check the law for suppressors, barrel length and hunting where you live and where you'll shoot.
4. If you own both, set up a system to keep the ammo and magazines apart. See the warning above.
5. Compare cost per round on the caliber pages, like for like. Product pages chart D.O.P.E. price history as retailer prices come in, so you can tell a real drop from a normal price. See how D.O.P.E. price history works.

Sources

• SAAMI, ANSI/SAAMI Z299.4-2025, Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Ammunition (300 AAC Blackout drawing issued 01/17/2011; 300 AAC Blackout and 223 Remington cartridge and chamber drawings: case lengths, rim and base dimensions, bullet and groove diameters, 2.260-inch maximum cartridge length; maximum average pressure of 55,000 psi for both; 24-inch standard test barrel, 16 inches for 300 AAC Blackout).
• SAAMI, Unsafe Firearm-Ammunition Combinations (technical data sheet, revised 8/24/2020; lists 300 AAC Blackout as unsafe in firearms chambered for 223 Remington; check the headstamp against the firearm's marking; a cartridge that fits isn't necessarily safe).
• SAAMI, Frequently asked questions (223 Remington and 5.56 interchangeability).
• Firearms News, The history of the 300 AAC Blackout cartridge (.221 Fireball, .300/.221 and .300 Whisper origins; AAC and Robert Silvers; SAAMI submission and naming; design goals; only a barrel change, with standard 5.56 bolts and magazines; supersonic and subsonic bullet weights and velocities; speed of sound of 1,126 fps in dry air at 68°F).
• Robert Silvers, Advanced Armament Corp., 300 AAC Blackout Low Visibility Carbine (National Defense Industry Association presentation; standard 5.56 case head and bolt face; full magazine capacity; subsonic and supersonic loads without adjustable gas; efficiency in short barrels; 110 gr TAC-RRLP velocity from 16-inch and 9-inch barrels).
• American Rifleman (NRA), The 300 Blackout: a knockout punch (5.56 as the dominant intermediate cartridge; 5.56 can fare poorly in shortened barrels and be difficult to suppress while keeping supersonic performance; 300 BLK uses a standard 5.56 bolt and magazine and converts mainly through a barrel change).
• Shooting Illustrated (NRA), 7.62x39 vs. .300 Blackout (.300 Whisper background; SAAMI approval issued January 17, 2011; a 5.56 barrel can be swapped for 300 Blackout with no other changes; standard AR magazines at full capacity).
• Federal Premium, American Eagle 5.56x45mm 55 gr FMJ BT (AE193), American Eagle 300 Blackout 150 gr FMJ BT (AE300BLK1) and American Eagle Suppressor 300 Blackout 220 gr OTM (AE300BLKSUP2) (published muzzle velocity, energy and 100-yard-zero trajectories; subsonic load for suppressed use; clean-burning powders).
• American Rifleman (NRA), Subsonic ammo 101: everything the suppressor shooter should know (speed of sound changes with temperature, humidity and altitude; supersonic ammo through a suppressor is substantially quieter than unsuppressed but keeps its crack; many subsonic rifle bullets don't expand at subsonic speed; subsonic reliability in AR-pattern rifles and gas-block adjustment).
• Hornady, 300 Blackout 110 gr V-MAX Hornady BLACK and 300 Blackout 190 gr Sub-X Subsonic (velocity and energy from a 16-inch test barrel; Sub-X bullet designed to expand at low velocities; subsonic loads for suppressed or unsuppressed use).
• Tactical Life (Athlon Outdoors), .300 Blackout vs 5.56 NATO: an examination for home defense (5.56's lower ammunition cost and 55 to 77 gr bullet range; 5.56 loses its advantages at subsonic speeds; rifles set up for subsonic may need buffer or gas changes for supersonic; suppressors and SBRs are prohibited in some places).
• MeatEater, 5.56 NATO vs. 300 Blackout: Caliber Battle (5.56 ahead on cartridge cost and availability; 55 gr and 77 gr 5.56 bullet weights; trajectory comparison; deer taken with 5.56/.223 and medium-game loads; coyote and varmint use; 300 Blackout on deer and hogs at shorter range; most subsonic ammo not designed for hunting).
• NRA Blog, Avoiding the .300BLK AR-15 "ka-boom!" (300 BLK chambers in a 5.56 rifle but must never be fired in it; ammo separation, magazine marking and one-caliber-per-trip practices).
• Windham Weaponry, Beware: .300 Blackout ammo can be chambered in a 5.56/.223 chamber with catastrophic results (rifles returned after firing 300 BLK in a 5.56/.223 chamber; mixed ammo on a shared bench).
• Magpul, PMAG 30 AR 300 B GEN M3 and its safety instruction guide (dedicated 300 BLK magazine; bullet profiles and reliability in 5.56 magazines; visual and tactile differences to prevent cross-loading).
• U.S. Code, 26 U.S.C. § 5845 (NFA definitions: rifles with barrels under 16 inches and silencers are "firearms" under the NFA).
• ATF, National Firearms Act (federal NFA overview and current guidance).

5.56 vs 300 Blackout FAQ

Can I shoot 300 Blackout in a 5.56 or .223 rifle?

No. Never. A 300 Blackout round can fit in a 5.56 magazine and close in a 5.56 chamber, but its .30-caliber bullet can't safely pass through a .22-caliber bore. Firing it can destroy the rifle and injure the shooter and people nearby. SAAMI lists 300 AAC Blackout as an unsafe cartridge in a firearm chambered for 223 Remington. Only fire ammunition that matches the marking on your barrel.

Do 5.56 and 300 Blackout use the same magazines?

Generally, yes. 300 Blackout was designed to feed from standard AR-15/M16 magazines at full capacity. Some shooters and manufacturers prefer dedicated 300 Blackout magazines, such as Magpul's PMAG 30 AR 300 B, because heavy subsonic bullets come in many shapes and a magazine that looks and feels different makes it harder to mix up the two cartridges. If you use the same magazine model for both, mark the 300 Blackout magazines clearly.

What do I need to change to switch an AR-15 from 5.56 to 300 Blackout?

The barrel. 300 Blackout uses the same bolt and magazines as 5.56, so the cartridge was designed to need only a barrel change. Some rifles, especially short or suppressed ones, also need gas or buffer tuning to run both supersonic and subsonic loads reliably. Follow the barrel or upper manufacturer's instructions, make sure the new barrel is clearly marked, and have a qualified gunsmith do the work if you aren't sure.

Is 300 Blackout more expensive to shoot than 5.56?

Usually, yes. Published comparisons from MeatEater and Tactical Life have found 5.56 practice ammo cheaper than 300 Blackout. That's a general pattern, not a guarantee, and prices move. The tables in this guide show cost per round for both from the best price we have: MSRP for now, retailer prices as they join Price Dope.

Is 300 Blackout subsonic?

It depends on the load. 300 Blackout comes in supersonic loads with lighter bullets and subsonic loads with heavy bullets. Hornady's 300 Blackout 110 gr V-MAX is rated at 2,375 fps from a 16-inch test barrel, well above the speed of sound, while Hornady's 190 gr Sub-X is rated at 1,050 fps and Federal's American Eagle Suppressor 220 gr OTM at 1,000 fps, both below it. Check the box or the manufacturer's data for the load you buy.

Do I need a suppressor to shoot subsonic 300 Blackout?

No. Subsonic 300 Blackout can be fired without a suppressor, and Hornady describes its subsonic loads as suited to suppressed or unsuppressed shooting. Without a suppressor you still need hearing protection; you just lose the bullet's supersonic crack. Some rifles need tuning to cycle reliably with subsonic ammo, so test it in yours. Suppressors are regulated under the National Firearms Act, so follow federal, state and local law.

Which is better in a short barrel?

300 Blackout was designed for it. AAC developed the cartridge to work well from short barrels and with suppressors, while American Rifleman notes that 5.56 can fare poorly in shortened barrels because it relies so much on velocity. Under federal law, a rifle with a barrel shorter than 16 inches is regulated under the National Firearms Act, and state and local laws vary, so check the law where you live before you buy or build one.

Does cost per round include shipping and tax?

No. On Price Dope, cost per round is the price divided by the number of rounds in the box. While a table is showing MSRP, it's the MSRP divided by the round count. Shipping, taxes and fees aren't included, so check the final price at checkout.

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