Not Just 9mm and 5.56: The Growing Appeal of Alternative Calibers

Quick Answer

9mm and 5.56 NATO aren't going anywhere.

They remain two of the most established cartridges in the American firearms market, supported by enormous selections of firearms, ammunition, magazines, and accessories. For most shooters, choosing a mainstream cartridge remains the simplest and often most economical option.

What's changing is that choosing something else no longer necessarily means accepting the inconveniences that once came with owning a niche caliber.

Cartridges such as 5.7×28mm, 10mm Auto, .300 Blackout, and 6mm ARC now occupy increasingly defined roles. More firearm manufacturers are chambering guns for them. Ammunition selection has expanded. Shooters also have clearer reasons for choosing them beyond simply wanting something different.

Each addresses a different requirement.

5.7×28mm has expanded from a cartridge primarily associated with FN into a much broader ecosystem of pistols and compact platforms.

10mm Auto has experienced a resurgence among handgun owners who want a more powerful semi-automatic option, particularly for hunting and outdoor applications.

The .300 Blackout established itself around short-barreled and suppressor-oriented platforms while maintaining compatibility with much of the AR-15 ecosystem.

And 6mm ARC targets shooters who want greater long-range capability from the AR-15-size platform than traditional 5.56 configurations typically provide.

The trend isn't about replacing the standards.

It's about cartridges becoming specialized enough—and sufficiently supported—that shooters can choose ammunition around a particular job rather than defaulting to the most common caliber available.

Key Takeaways

• 9mm and 5.56 NATO remain the standards. Alternative cartridges are expanding the market rather than replacing its most established options.
• 5.7×28mm is one of the clearest niche-to-mainstream stories, with a growing selection of handguns, PDW-style firearms, carbines, and factory ammunition.
• 10mm Auto proves an alternative caliber doesn't need to be new. Modern pistols and renewed interest in hunting and outdoors-oriented handguns have helped revive a decades-old cartridge.
• .300 Blackout succeeded because it addressed a specific platform requirement, particularly compact and suppressor-oriented AR-pattern firearms.
• Firearm and ammunition support determine whether alternative calibers survive. Interesting ballistics aren't enough if ammunition remains difficult or expensive to obtain and manufacturers stop chambering firearms for the cartridge.

Why Shooters Are More Willing to Try Different Calibers

For a long time, buying an unusual cartridge involved accepting some significant disadvantages.

The firearm itself might be difficult to find. Factory ammunition could be limited to a handful of loads. Local stores might not stock it. Magazines and replacement components could be uncommon, and ammunition prices might discourage regular practice.

Those considerations still matter.

But several alternative cartridges have now reached enough market penetration that they no longer feel particularly exotic.

Walk into a well-stocked gun store and finding 10mm or .300 Blackout ammunition isn't unusual. 5.7×28mm ammunition is offered by considerably more manufacturers than when FN platforms dominated the caliber. Even newer rifle cartridges can build meaningful ecosystems surprisingly quickly when major ammunition and firearm manufacturers support them.

The internet has also changed the equation.

Shooters aren't entirely dependent on whatever three calibers happen to occupy the most shelf space at the nearest sporting-goods store. Wider product availability makes owning a less-common cartridge considerably easier than it once was.

Still, availability shouldn't be confused with affordability.

A cartridge can become mainstream enough to own conveniently without becoming inexpensive enough to shoot frequently.

That's an important distinction when deciding whether an alternative caliber actually makes sense.

Alternative Doesn't Mean Better

One of the easiest mistakes in caliber discussions is treating cartridges like generations of technology.

A newer cartridge isn't automatically an upgrade over an older one.

5.7×28mm doesn't make 9mm obsolete.

6mm ARC doesn't make 5.56 NATO obsolete.

And .300 Blackout doesn't make every other AR-15 cartridge unnecessary.

They were developed around different priorities.

A shooter who buys an alternative caliber because it addresses a specific requirement can end up with a very useful firearm. Someone who buys it simply because the cartridge is newer or currently popular may discover that the conventional option would have been cheaper and easier to support.

That makes intended use the most important part of the buying decision.

5.7×28mm: From Specialized Cartridge to Growing Platform

Few cartridges demonstrate the changing market better than 5.7×28mm.

For years, American shooters primarily associated 5.7 with two FN firearms: the Five-seveN pistol and PS90, the civilian counterpart to the P90 platform. That gave the cartridge an enthusiastic following, but it remained relatively specialized.

That market looks very different today.

Ruger, Smith & Wesson, PSA, KelTec, Tisas, and other manufacturers have introduced 5.7×28mm firearms, giving buyers choices across conventional handguns, larger-format pistols, and PDW-style platforms. Ammunition manufacturers have responded with additional factory loads.

The appeal isn't simply magazine capacity.

5.7×28mm offers relatively mild recoil and a small, lightweight cartridge, characteristics that work particularly well in high-capacity handgun and compact-platform designs. Its bottlenecked case and high-velocity approach also make it fundamentally different from conventional service-pistol cartridges.

But buyers should be careful about treating 5.7 as a direct substitute for 9mm based on velocity or capacity alone.

Ammunition cost, firearm size, intended use, projectile construction, and terminal performance of the specific load all matter. Different 5.7 factory loads can be designed for very different purposes.

The more significant story is that shooters interested in 5.7 are no longer buying into a two-firearm ecosystem.

5.7×28mm is becoming a platform category.

That is a major step toward a formerly specialized cartridge becoming a sustainable mainstream alternative.

10mm Auto: The Alternative Caliber That Came Back

If 5.7 represents expansion, 10mm Auto represents revival.

The cartridge dates back decades and has experienced several periods of changing popularity. For years, .40 S&W occupied much more of the mainstream semi-automatic handgun market while 10mm remained associated with enthusiasts, hunters, and shooters who specifically wanted its capabilities.

Today, the situation has changed considerably.

Major manufacturers now offer modern 10mm pistols, including configurations based on familiar striker-fired and 1911-style platforms. Ammunition companies support the caliber with everything from practice ammunition to loads marketed toward hunting and outdoor applications.

That broader ecosystem has made 10mm substantially easier for an average handgun buyer to consider.

Its appeal is also relatively straightforward: 10mm can offer considerably more energy than common service-pistol cartridges depending on the factory load, while retaining the capacity and operating characteristics of a semi-automatic handgun.

But 10mm demonstrates another important lesson about alternative calibers:

The performance has a cost.

Full-power loads can produce greater recoil, ammunition is generally more expensive than 9mm, and pistols chambered in 10mm often require larger frames and slides.

For someone primarily interested in inexpensive range practice or ordinary concealed carry, those characteristics may provide little benefit.

For a shooter specifically seeking a powerful semi-automatic handgun for hunting or outdoor use where lawful and appropriate, the equation can look very different.

10mm isn't gaining ground because everyone suddenly needs more handgun. It's gaining ground because manufacturers are giving the shooters who do want that capability better firearms to choose from.

.300 Blackout: What Happens When a Niche Cartridge Finds Its Job

The success of .300 AAC Blackout may provide the best blueprint for how an alternative cartridge becomes established.

Rather than trying to replace 5.56 NATO everywhere, .300 Blackout developed a strong identity around short-barreled firearms, suppressor use, and the AR-15 platform.

That clearly defined role mattered.

The cartridge fits the standard AR-15-size platform and uses the same bolt face as 5.56/.223. It was also designed to function with standard AR-15 magazines, although dedicated .300 Blackout magazines are available and can provide improved compatibility with some longer, heavier subsonic loads.

Those load types behave very differently, and buyers need to understand that distinction rather than treating ".300 Blackout" as one uniform ballistic profile. But the availability of both helped the cartridge establish itself among shooters interested in compact and suppressed platforms.

There is also an important safety consideration.

Because .300 Blackout and 5.56 ammunition can be used around firearms with otherwise similar AR components, careful ammunition and firearm identification is essential. Because .300 Blackout and 5.56 ammunition can be used around firearms sharing otherwise similar AR components and magazines, careful ammunition and firearm identification is essential.

A .300 Blackout cartridge can create a catastrophic hazard if mistakenly loaded and fired in a 5.56/.223 firearm. Clearly separating and identifying ammunition, magazines, and firearms is therefore particularly important when owning both calibers.

6mm ARC: Getting More From the AR-15 Platform

6mm ARC approaches the alternative-caliber question from another direction.

Rather than focusing on an extremely short rifle, the cartridge was designed to provide useful ballistic performance from the AR-15-size platform, particularly as distances increase.

That makes it appealing to shooters who want to retain the relatively compact dimensions of an AR-15-based rifle while using heavier, higher-ballistic-coefficient 6mm projectiles than typical 5.56 loads.

The tradeoff is that adopting 6mm ARC requires more specialized components than simply changing ammunition.

The rifle needs the appropriate barrel, bolt, and magazines, and ammunition availability is nowhere near the scale of 5.56 NATO.

That means 6mm ARC makes the strongest case when the shooter actually needs what the cartridge provides.

For someone shooting primarily at shorter distances with inexpensive ammunition, 5.56 remains difficult to beat.

For a hunter or precision-oriented shooter who wants different external-ballistic characteristics while remaining within an AR-15-size platform, 6mm ARC becomes considerably more interesting.

And that's exactly the pattern we're seeing across the alternative-caliber market:

Specialization is becoming a selling point rather than a liability.

Four Alternative Calibers Compared

The table makes the larger point clear.

These cartridges aren't competing for exactly the same customer.

And that's precisely why alternative calibers are gaining ground.

Shooters aren't necessarily searching for a new universal standard. They're increasingly able to buy a cartridge specifically suited to the firearm and application they have in mind.

What Makes an Alternative Caliber Worth Buying?

The expanding cartridge market creates more choices, but it also creates more opportunities to buy into a caliber that looks better on paper than it does for your actual needs.

Before choosing something outside the mainstream, evaluate the entire ecosystem surrounding the cartridge, not just its ballistic specifications.

Ammunition Availability Comes First

A firearm isn't particularly useful if you rarely want to shoot it because ammunition is difficult to find or prohibitively expensive.

9mm and 5.56 NATO have enormous advantages here. Multiple manufacturers produce large quantities of practice, defensive, hunting, and specialty loads, depending on the cartridge.

Alternative calibers vary considerably.

10mm and .300 Blackout have developed broad commercial support. 5.7×28mm has expanded substantially as additional firearms have entered the market. 6mm ARC is established enough to have multiple factory ammunition options, but it remains much less ubiquitous than 5.56.

Before buying, look beyond whether ammunition is available today.

Ask whether several established manufacturers support the cartridge. A caliber with multiple ammunition suppliers is generally less dependent on the fortunes of one firearm or manufacturer.

Practice Cost Matters More Than Many Buyers Expect

A cartridge may offer exactly the performance you want, but the economics still matter.

Consider someone choosing between a mainstream 9mm pistol and a 5.7×28mm pistol. Even if the 5.7 platform has characteristics that appeal to that shooter, ammunition cost can influence how frequently the firearm actually gets used.

The same issue appears with rifles.

A .300 Blackout owner who wants regular range time may spend substantially more on ammunition than someone shooting common 5.56 loads. Specialized 6mm ARC ammunition can likewise make high-volume practice more expensive.

This doesn't make the alternative cartridge a bad purchase.

It simply means the ammunition budget belongs in the buying decision before the firearm comes home.

Firearm Selection Can Make or Break a Cartridge

A successful cartridge needs guns people actually want to own.

5.7×28mm is a particularly good example. Its recent growth isn't happening because the cartridge suddenly changed. The selection of firearms chambered for it changed.

Buyers can now choose among traditional handguns, larger-format pistols, compact PDW-style firearms, and carbines from multiple manufacturers.

10mm has benefited from a similar effect. Shooters no longer have to seek out a relatively narrow selection of specialized pistols. Major manufacturers have brought the cartridge into familiar modern handgun platforms.

This creates a reinforcing cycle:

More firearms attract more shooters. More shooters create greater demand for ammunition. Better ammunition support makes manufacturers more willing to introduce additional firearms.

That's how a niche caliber starts becoming a sustainable category.

Don't Ignore Magazines and Replacement Parts

The cartridge itself is only part of the ecosystem.

Before committing to an alternative caliber, consider:

• Magazine availability and cost
• Replacement components
• Manufacturer support
• Optics and accessory compatibility
• Gunsmith familiarity
• Number of firearms chambered for the cartridge

This becomes especially important with rifle cartridges requiring caliber-specific bolts or magazines.

A mainstream cartridge benefits from decades of infrastructure. An alternative caliber has to build that infrastructure over time.

For buyers planning to keep a firearm for many years, ecosystem depth can matter almost as much as ballistic performance.

Specialized Cartridges Work Best for Specialized Requirements

The strongest alternative calibers usually have a clear answer to one question:

Why does this cartridge exist?

For .300 Blackout, the answer includes compact AR-pattern firearms and suppressor-oriented applications.

For 6mm ARC, it includes obtaining different longer-range ballistic characteristics from an AR-15-size platform.

For 10mm, the attraction includes a more powerful semi-automatic handgun cartridge for shooters whose applications justify it.

For 5.7×28mm, low recoil, lightweight ammunition, magazine capacity, and compact firearm designs form much of the appeal.

Those are understandable reasons to choose something different.

Problems arise when buyers reverse the process—purchasing an unusual caliber first and then trying to invent a requirement for it afterward.

When the Mainstream Cartridge Is Still the Better Choice

Alternative calibers are becoming easier to recommend, but the boring answer is sometimes still the correct one.

Choose the Mainstream Option When Cost Is Critical

For frequent range use, common cartridges generally benefit from stronger competition among ammunition manufacturers and greater production volume.

A modest difference in price per round becomes significant over thousands of rounds.

Choose It When Availability Matters Most

If you want the greatest likelihood of finding ammunition at local sporting-goods stores, established cartridges maintain a substantial advantage.

This can matter particularly when traveling.

Choose It When the Alternative Doesn't Solve a Problem

There is little reason to accept higher ammunition costs, fewer firearm choices, or specialized components if the alternative cartridge doesn't provide a capability you actually need.

A shooter whose AR is primarily used for ordinary range shooting at moderate distances may gain relatively little from converting to a specialized cartridge.

Likewise, someone satisfied with a 9mm carry pistol doesn't need to move to 5.7 simply because the caliber is receiving attention.

Differences are only useful when the difference matters.

Alternative Caliber or Passing Trend?

This is the difficult part of buying into an emerging cartridge.

Firearms history contains plenty of cartridges that generated considerable excitement before becoming difficult to find.

No one can guarantee which current calibers will remain popular decades from now, but there are several encouraging signs buyers can look for.

Multiple Ammunition Manufacturers

One ammunition company supporting a cartridge is very different from widespread production across the industry.

Broader support creates competition and makes the caliber less dependent on a single manufacturer.

Multiple Firearm Platforms

A cartridge available in one proprietary firearm has a much narrower foundation than one supported across several handgun or rifle families.

This is one reason the expansion of 5.7×28mm is significant.

A Clearly Defined Purpose

Cartridges tend to have stronger staying power when they provide a recognizable capability rather than relying primarily on novelty.

Continued Product Development

New firearm introductions, new factory loads, and continued manufacturer investment are healthier signals than online attention alone.

A cartridge doesn't become established because people are talking about it.

It becomes established when companies keep making guns and ammunition for it—and shooters keep buying both.

The Four Cartridges Aren't at the Same Stage

It's also important not to describe 5.7×28mm, 10mm, .300 Blackout, and 6mm ARC as though they occupy identical positions in the market.

They don't.

10mm Auto is an old cartridge experiencing renewed popularity.

.300 Blackout has already moved well beyond experimental or niche status and has developed a substantial commercial ecosystem.

5.7×28mm is undergoing substantial platform expansion, moving from a relatively specialized market into a much broader selection of firearms.

6mm ARC remains more specialized, with much of its appeal centered on shooters who specifically want its capabilities from an AR-15-size platform.

That distinction matters because "alternative caliber" covers everything from an established cartridge outside the dominant mainstream to a comparatively young option still building its market.

Should You Add an Alternative Caliber to Your Collection?

Start with three questions.

What does it give me that my current caliber doesn't?

There should be a meaningful answer—whether that's platform size, recoil characteristics, ballistic performance, suppressor-oriented use, or another legitimate requirement.

Can I afford to shoot it as much as I intend to?

Look at realistic ammunition costs, not just the price of the firearm.

Is the ecosystem strong enough for how long I expect to own it?

Consider ammunition manufacturers, firearm selection, magazines, parts, and continued industry support.

If the answers make sense, buying outside the traditional standards can be entirely reasonable.

If they don't, there is nothing outdated about choosing 9mm, 5.56 NATO, .308 Winchester, or another established cartridge.

The growing alternative-caliber market isn't making those standards irrelevant.

It's giving shooters more specialized choices when the standards aren't the best fit for a particular job.

And that may be the most important reason this trend looks more durable than another short-lived caliber race.

Final Thoughts: More Choices, Not New Standards

The growth of alternative calibers doesn't mean shooters are abandoning 9mm, 5.56 NATO, or other established cartridges.

It means the market has become large enough to support more specialized choices.

5.7×28mm is benefiting from an expanding selection of firearms and ammunition. 10mm Auto has found renewed relevance among shooters looking for greater handgun performance for particular applications. .300 Blackout has established a clear role in compact and suppressor-oriented platforms. And 6mm ARC gives AR-15 owners another option when longer-range ballistic performance is a priority.

None of them needs to replace an existing standard to be successful.

That's the important shift.

A decade or two ago, choosing an uncommon cartridge could mean accepting limited firearms, expensive ammunition, and uncertain long-term support. Today, several alternative calibers have developed ecosystems substantial enough to make them practical choices rather than curiosities.

But buyers should still start with the application.

Choose the cartridge because it solves a problem—not because it's different.

If 9mm or 5.56 does everything you need at lower cost with greater availability, there is little reason to complicate things. If another cartridge provides a capability that matters to you, however, today's market offers more viable alternatives than ever.

Some alternative calibers have also benefited from the growing popularity of compact firearm platforms. .300 Blackout performs particularly well from relatively short AR barrels, while 5.7x28mm has expanded into an increasingly diverse collection of pistols and compact carbines. .300 Blackout's ability to work effectively from short barrels is one reason it has become so closely associated with compact AR configurations. If portability is part of what attracts you to these cartridges, our guide to the truck gun concept explores how compact rifles and pistols fit into the broader vehicle-carry discussion.

Frequently Asked Questions

Are alternative calibers replacing 9mm and 5.56?

No. 9mm and 5.56 NATO remain deeply established, with enormous firearm and ammunition support. Alternative cartridges primarily give shooters additional choices for more specialized applications.

Is 5.7×28mm becoming mainstream?

It is considerably more mainstream than it once was. Multiple firearm and ammunition manufacturers now support 5.7×28mm, expanding the cartridge well beyond the FN platforms historically associated with it. Whether it reaches the availability or pricing of 9mm is a different question.

Why has 10mm Auto become popular again?

Modern firearm selection has helped. Shooters now have considerably more 10mm pistols to choose from, while the cartridge continues to appeal to hunters and outdoors-oriented handgun owners who want its particular performance characteristics.

Is .300 Blackout still considered an alternative caliber?

It is well established today, but it remains an alternative to 5.56 for shooters seeking different capabilities from an AR-15-size platform. Its strong association with short-barreled and suppressor-oriented firearms helped it develop a clearly defined role.

What should I consider before buying a less-common caliber?

Look at ammunition price and availability, firearm selection, magazines and parts, manufacturer support, and what the cartridge actually provides for your intended use. A strong long-term ecosystem can be just as important as ballistic specifications.

About the Author

The ProArmory editorial team includes experienced hunters, competitive shooters, military veterans, firearms instructors, and firearms industry professionals committed to producing accurate, practical, and research-based content. Our articles draw on manufacturer specifications, current industry information, and real-world shooting and hunting experience to help readers make informed decisions about firearms, ammunition, optics, hunting gear, and related equipment.

Disclaimer

This article is intended for informational and educational purposes only. Cartridge performance varies by firearm, barrel length, ammunition manufacturer, projectile, and specific load. Always use only ammunition of the correct caliber and specification for your firearm and follow the firearm and ammunition manufacturers' instructions.

Firearm, ammunition, magazine, hunting, carry, and transportation laws vary by jurisdiction and may change. Verify current federal, state, and local requirements applicable to your intended use. Always follow established firearm-safety practices.