5.56 NATO vs .300 Blackout

Same rifle, same magazines, very different cost per round — here is what the live price data says about which cartridge earns its place in your AR.

AmmoSpotter Research Desk By AmmoSpotter Research Desk
Published Reviewed October 2026 7 min read
5.56 NATO vs .300 Blackout

Which cartridge is actually cheaper to shoot?

This is the deciding factor for most people, and it is the one most comparisons skip because they have no way to answer it. We track live retail listings across every retailer we carry and normalize each one to cost per round, so the question has an actual answer rather than an opinion.

Here is what each cartridge costs right now.

5.56x45mm NATO Price Index

Live · Oct 22, 2026
Market floor / round
$0.480
Market average
$0.867
Lowest box price
$8.99
30-day trend
▼ 2.2%
Compare all 5.56x45mm NATO deals by cost per round →

.300 Blackout Price Index

Live · Oct 22, 2026
Market floor / round
$0.700
Market average
$1.525
Lowest box price
$12.89
30-day trend
▼ 0.5%
Compare all .300 Blackout deals by cost per round →

Look at the floor on each, not just the average. The floor is what a disciplined buyer actually pays; the average is inflated by premium hunting and defensive loads that most people shoot rarely. On both measures, .300 Blackout sits above 5.56 — and it stays there. This is not a sale you wait out.

The gap compounds faster than people expect. Run the two floor numbers from the blocks above through the calculator against whatever your annual round count actually is:

Cost Per Round Calculator

The only number that matters when comparing ammo. Shipping included.

Your true cost per round
$0.500

If you are unsure what your annual round count should be, how many rounds it takes to get good is the honest version of that math. For most shooters the answer is high enough that a per-round premium turns into a serious annual number.

Why .300 Blackout costs more (and always will)

The price gap is not a supply glitch. It comes from three structural facts.

No military contract, no surplus. 5.56 is produced at enormous scale for government contracts worldwide, and that scale sets the commercial floor. Surplus and contract-overrun M193 and M855 land in the retail channel constantly. .300 Blackout has no equivalent pipeline. Every round is made for the commercial market.

More bullet, more lead. A typical .300 Blackout projectile is substantially heavier than a 55- or 62-grain 5.56 bullet — often two to four times the mass in the subsonic loads. Component cost scales with that.

Lower volume. Fewer lines run it, fewer retailers stock it deep, and it rarely gets the loss-leader treatment that pulls 5.56 case prices down.

Those are the same forces described in why ammo prices move, applied to a cartridge that sits on the wrong side of all of them. Expect the spread to persist.

What .300 Blackout was designed to do

.300 Blackout was not built to replace 5.56 as a general-purpose cartridge. It was built to solve a narrow problem: get .30-caliber performance out of an AR-15 that keeps its standard bolt and magazines, and do it from a very short barrel.

That last part matters more than most buyers realize. 5.56 is a high-pressure, high-velocity cartridge that depends on barrel length to reach its designed velocity. Chop it down to 9 or 10 inches and you give up real performance while gaining an enormous muzzle blast. .300 Blackout reaches essentially full powder burn in that same short barrel. It was engineered around the constraint.

The corollary is the part people skip: if your rifle has a 16-inch barrel, you are not buying that advantage. You are paying the premium for a benefit your build does not use. At that length, 5.56 is doing what it was designed to do, and the comparison collapses into a straight cost question — which 5.56 wins.

Does .300 Blackout actually hit harder?

Supersonic .300 Blackout throws a heavier bullet at lower velocity than 5.56. That is a different terminal profile, not a strictly better one, and how it behaves depends entirely on the projectile.

We do not run our own terminal ballistics testing, and you should be skeptical of any retailer or aggregator that claims it does. What we will say is that published protocols exist for exactly this question, and load-specific results from those protocols are the only thing worth reading. A caliber does not have terminal performance; a specific load does.

The general shape of it is uncontroversial: for barrier-heavy or longer-range work, 5.56's velocity and the enormous variety of available projectiles give it more useful options. For short-barrel work inside typical defensive distances, a well-chosen supersonic .300 Blackout load is doing something reasonable. Neither statement justifies the price gap on its own. We are explicit about what we will and will not claim about a cartridge, and terminal superiority is firmly in the second category.

If home defense is your actual use case for an AR, read why FMJ is the wrong default for a defensive 5.56 build before you switch calibers to solve a problem your load selection is causing.

The suppressor case: this is where .300 Blackout earns it

Here is the one argument that survives contact with the price data.

Subsonic .300 Blackout was designed from the start to run heavy bullets below the speed of sound while still cycling an AR reliably. That combination — suppressor-host, subsonic, semi-automatic, standard magazines — is genuinely difficult to achieve with 5.56. Subsonic 5.56 is a niche handloading exercise, not something you buy off a shelf and shoot reliably.

If you own a can and the reason you own it is to actually shoot quietly rather than just to take the edge off, .300 Blackout is the mainstream answer. You are not paying a premium for a marginal ballistic difference; you are paying for a capability 5.56 does not offer at retail.

Note the trade-off out loud: subsonic loads are the most expensive part of the .300 Blackout catalog, not the cheapest. The capability costs money on top of a caliber that already costs more. Our guide to ammo for suppressed shooting covers what actually goes quiet across calibers and where the subsonic premium is worth paying.

Cheapest .300 Blackout Right Now

Prices updated Oct 22, 2026
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What does converting an AR-15 to .300 Blackout cost?

Less than people assume, because almost nothing changes. Same lower receiver. Same bolt and bolt carrier group. Same buffer system. Same STANAG magazines. You need a .300 Blackout barrel — practically, a complete upper, unless you are comfortable headspacing your own.

That low conversion cost is the trap. The barrel is a one-time expense; the ammunition is forever. Before you buy the upper, price out a realistic year of shooting at the two floor numbers above. For most people the ammunition delta exceeds the cost of the upper within the first year.

If the appeal is a second upper rather than the cartridge specifically, be honest about that. And if the plan is to shoot enough .300 Blackout to justify it, run the reloading numbers — low-volume commercial cartridges are exactly where handloading economics look best.

The safety problem you cannot design around

.300 Blackout is 5.56 brass necked up to .30 caliber. It uses the same magazines. It will drop into a magazine full of 5.56 and it will feed.

A .300 Blackout round will chamber in a 5.56 barrel. Firing it destroys the rifle and can injure the shooter. This is a documented, repeatable failure mode, not a rare fluke, and it is the single most important thing to understand before you own both.

So which one should you buy?

Buy 5.56 if you shoot volume, your barrel is 14.5 inches or longer, you do not own a suppressor, or your budget has a ceiling. This covers most AR owners. Start with our 5.56 and .223 ammo guide, and note that .223 and 5.56 are not interchangeable in the direction most people assume — that distinction saves more money than caliber-switching does.

Buy .300 Blackout if you own a suppressor and intend to shoot subsonic through it, or your build is short enough that 5.56 is being wasted. Those are real reasons. Everything else is a preference you are entitled to have, as long as you price it honestly.

Buy both if you already own the AR and want a second upper for a specific job. Just budget the ammunition, not the barrel.

Before you order either, check where you can actually have it shipped — restrictions vary by state and locality, they change, and you should verify the current rules for your address rather than trusting any list, including ours.

Cheapest Bulk 5.56 Right Now

Prices updated Oct 22, 2026
See all matching deals →

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Frequently Asked Questions

Is .300 Blackout more expensive than 5.56?+
Yes, consistently and by a wide margin. Both the cheapest listing and the catalog average for .300 Blackout sit well above 5.56 in our live index, and the gap holds across brands. The live price blocks in this article show both numbers side by side so you can check the spread yourself before you commit to a caliber.
Can I shoot .300 Blackout in my 5.56 upper?+
No. .300 Blackout requires its own barrel. The bolt, bolt carrier, buffer, lower and magazines carry over from a standard AR-15, so a conversion is a barrel or complete-upper swap rather than a new rifle. Never attempt to fire .300 Blackout from a 5.56 chamber.
Do 5.56 and .300 Blackout use the same magazines?+
Yes, standard STANAG AR-15 magazines feed both. That compatibility is exactly why the two rounds get mixed up, and it is why loose .300 Blackout in a range bag next to 5.56 is genuinely dangerous. Label and segregate your magazines if you own both uppers.
Is .300 Blackout worth it if I do not own a suppressor?+
Usually not, on cost alone. Unsuppressed and supersonic, .300 Blackout mostly buys you better performance from very short barrels and a heavier bullet, while you pay a real premium per round. If you shoot high volume from a 16-inch barrel with no can, 5.56 is the more rational purchase.
Why is .300 Blackout so much more expensive per round?+
It is a lower-volume commercial cartridge with no military contract production behind it and almost no surplus supply, so it never gets the manufacturing scale that drives 5.56 pricing down. It also uses a heavier bullet and more of it. The structural forces behind that gap are the same ones that move every ammo price.
What barrel length does .300 Blackout actually need?+
It was designed to reach full powder burn in a short barrel, which is why it is popular on pistol-length and SBR builds. 5.56 loses meaningful velocity as barrels get shorter. If your build is 16 inches or longer, the primary argument for .300 Blackout largely disappears.
Topics .223 / 5.56 NATO .300 Blackout AR-15 Cost Per Round Subsonic Ammo Suppressed Shooting

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AmmoSpotter Research Desk

About the author

AmmoSpotter Research Desk

Price & Ballistics Research

The AmmoSpotter Research Desk analyzes live retail pricing across every ammunition, firearm and accessory listing we track. Recommendations here are ranked against real cost-per-round data pulled daily from the retailers we monitor - not against manufacturer marketing copy.

  • ✓Tracks 180,000+ live product listings across 6 retailer feeds
  • ✓Records price history on every listing, every day
  • ✓Cost-per-round methodology applied to all ammunition rankings
  • ✓No product is ranked without a verifiable in-stock retail price
  • ✓Affiliate relationships never influence rankings

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