Silencers 101
300 Blackout: Shooting with Subsonic Ammo

300 Blackout: Shooting with Subsonic Ammo

300 Blackout

One of the hottest new rounds to emerge in the past few years is 300 Blackout; this is a true dual-purpose intermediate sized cartridge that can be fired in both subsonic and supersonic loads. It was designed to be used in AR-pattern rifles with only a barrel change to convert a traditional AR-15 rifle from 5.56 NATO. It has since become one of the most popular rounds to use with a suppressor.

This relatively new cartridge has been around a bit longer than some might think and has its share of fans and detractors, but 300 Blackout has more than proven itself as a hunting, defensive and target round in that time. It may not be the be-all and end-all cartridge, but for most shooters and hunters, 300 Blackout is worth taking a second look at.

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What is 300 Blackout Ammo?

The 300 Blackout round has its roots in the 300 Whisper cartridge designed by JD Jones of SSK Industries in the early 1990s. Jones formed the brass from 221 Fireball cases expanded to take a .30 caliber bullet. By varying the load, lighter bullets could be fired at supersonic levels with the power of the Soviet 7.62 x 39 or used with heavier bullets at a subsonic level for use with a sound suppressor.

Unfortunately, the round was trademarked by SSK and other manufacturers were unable to manufacture barrels or even brass and dies for the round. The 1994 Federal Crime Bill and Assault Weapon Ban did not help the subsonic cause, either, as threaded barrels on semi automatic rifles made them subject to the ban. National Firearm Act laws governing the sales of silencers were also misunderstood at the time and silencer ownership was a mere sliver of what it is today.

It seemed as if the round was doomed to die in the “also-ran” wildcat category until the Federal Assault Weapon Ban was allowed to sunset in 2004 and a company called Advanced Armament Corporation (AAC) began to show interest in the 300 Whisper.

AAC was eventually bought out by Remington Defense and the two companies worked on the design as a potent new caliber that could address perceived shortcomings with the 5.56 NATO round.

Remington and AAC changed the design slightly by using trimmed and expanded 5.56 NATO brass as opposed to 221 Fireball or 222 Remington as the parent case. They normalized different load data and submitted the new cartridge to SAAMI (Small Arms Ammunition Manufacturers Institute) and CIP (Permanent International Commission for the Proof of Small Arms) for standardization and christened the new round 300 AAC Blackout by CIP and 300 BLK by SAAMI.

The improved design means that it will work with a standard AR15 or M16 bolt and magazines with the only real part change being the barrel. Another positive note is that 300 Blackout and the original 300 Whisper cartridge are completely interchangeable from barrels to reloading dies as well as reloading components and specifications.

As a result of its popularity we have even seen the retail price of 300 Blackout ammunition decrease over time. This is always a good sign with regard to the longevity of an ammunition cartridge in the market.

Performance and Ballistics

In its standard form as a subsonic round, 300 Blackout most closely resembles the 7.62 x 39mm round first used in the SKS and AK-47 rifles of the former Soviet Union. In its subsonic loading it has been compared with both subsonic 9mm and 45 ACP.

One of the main reasons that the US Military was looking for a replacement round for 5.56 NATO was the loss of energy and velocity by the 5.56 NATO round as it was fired through barrels that were increasingly getting shorter.

The 5.56 round was developed for use in 20” barreled rifles. Severe deficiencies were found when trying to make the military service rifle shorter. Additionally, the use of a suppressor dictated going to a shorter barrel as soldiers were finding full sized rifles becoming unwieldy with a 5” to 8” sound suppressor mounted on the muzzle. Another consideration here was the effect of the initial blast of unburnt powder and flash increasing wear on the initial baffle of a 5.56 suppressor.

300 Blackout was optimized to be fired through shorter barrels and even in supersonic loadings it did not have that initial blast problem. The round exceeded most military expectations for the caliber in both subsonic and supersonic renderings.

On the civilian side, 300 Blackout has proven to be a performer in the field for hunting and on the competitive shooting circuit.


Every new cartridge is often compared to an older one and 300 Blackout is no exception. These comparisons are both a good thing and a bad thing for a few reasons.

On the good side, hunters and shooters generally want an idea of how a new round will perform. Comparing 300 BLK to an existing round with regards to bullet weight, caliber, velocity and energy sets the stage.

So the 300 Blackout supersonic loads are compared to rounds such as 30-30 Winchester and 7.62 X 39mm. This gives a shooter an idea of what to expect recoil wise and the intended use of the round.

Another consideration for rifle shooters is often the size of the rifle’s action. While this was addressed initially by use of 300 Blackout in the AR-15 or M16 platform with regard to bolt face, magazine configuration, etc, it is also an important consideration for use in a bolt action rifle.

For the bolt action rifle shooter, action length is often an important consideration, as this can affect the weight of the rifle and its overall configuration for handling recoil. Typical bolt action lengths are referred to as short, long and Magnum. The long action is used for rifles chambered in calibers such as 30-06 Springfield. Magnum actions are intended for powerful belted magnum cartridges such as 300 Winchester Magnum, 459 Winchester Magnum or 375 Holland & Holland. The short action is intended for everything from 17 Remington up to 308 Winchester and this is the size needed for a bolt action rifle chambered in 300 Blackout.

The subsonic 300 Blackout loads are often compared to 45 ACP, 10 mm or 9mm subsonic rounds. This showcases the dual purpose of the round. The advantage of 300 Blackout is if the shooter wants an AR-pattern rifle or pistol that is easily suppressed, they can use a common magazine and typically only need to swap an upper receiver. Pistol caliber conversions for the AR platform often need different magazines, buffer assembles and other changes to make them effective and reliable.

Where it becomes a bad thing is that these comparisons rarely give the complete picture to the shooter or hunter and can actually be a disservice to 300 Blackout and to the round to which it is being compared.

300 Blackout vs. 556

The most obvious comparison for 300 Blackout will be made with 5.56 NATO. After all, this is the round it was intended to dethrone.

As we stated earlier, this is a disservice to both cartridges. The 5.56 NATO round has a longer range, higher velocity and some would say more inherent accuracy. In its supersonic loading, 300 Blackout shares similar characteristics with the 7.62 X 39mm round which has often been set up as the rival of 5.56 NATO for the past 60 years.

Terminal ballistics for both rounds as a military cartridge will be compared ad nauseum. A lighter bullet in the form of 5.56, by as much as two to 3 times the weight, travelling at 75% to 100% of the velocity has its advantages over the heavier and slower 300 Blackout. Yet some troops would say that a heavier and slower bullet may not have the penetration ability of the 5.56 but addresses the overpenetration issues noted by US Army Rangers and Infantry in operations in Somalia where the 5.56 required multiple hits on target to dispatch an enemy soldier, whereas the 7.62 x 39mm seemed more effective at stopping an enemy combatant with a single round.

One of the dangers of keeping both rounds in the same collection is that 300 Blackout will actually chamber in a 5.56 rifle. It cannot be safely fired from that platform without causing a catastrophic failure to the firearm and injury or possibly death to the shooter and those in close proximity.

For this reason, we recommend that if you shoot both calibers to incorporate some variables with regard to your shooting components and accessories. For example, use one type or color of a magazine for one round and a different one for the other. This can be taken a step further by loading 300 Blackout subsonic rounds in a different magazine size from the 300 Blackout supersonic rounds so that a supersonic round does not accidentally go through a pistol caliber or 300 BLK subsonic rated suppressor accidentally.

The key advantage here is that AR magazines are inexpensive when compared to just about every other platform out there. This is another inherent advantage of 300 Blackout.

It is not a bad idea to ensure that the upper receivers can be easily distinguished, whether by different optics, rails or colors.

300 Blackout vs. 350 Legend

When 350 Legend debuted, Winchester claimed it was the fastest straight wall cartridge ever released. Like 300 Blackout ammunition, it had the ability to be loaded to subsonic or supersonic levels and it would fit in a standard AR15 action and magazine. Some hunters speculated that it would sound the death knell for 300 Blackout due to the fact that hunters in some north eastern and midwestern states were limited to hunting deer with a straight wall cartridge.

As fine a cartridge as it is, 300 Blackout had the advantage in that it had more than a 10-year head start on 350 Legend. There are simply more barrels, magazines, rifles, pistols and other accessories dedicated to 300 Blackout as opposed to 350 Legend.

350 Legend certainly has the upper hand as a hunting caliber in states where bottleneck cartridges are prohibited for big game hunting and performs well on animals like deer and black bear, but it will not overtake 300 Blackout on the whole anytime soon.

The other disadvantage is the limited amount of .35 caliber suppressors made for the supersonic load in 350 Legend. Subsonic 350 Legend can be safely fired through most 9mm suppressors in the same manner as 300 Blackout subsonic.

300 Blackout vs. 223

While 5.56 NATO and 223 Remington are used interchangeably, they are not the same round. The 5.56 NATO is loaded to a higher pressure level than 223 Remington. Furthermore, 223 Remington is considered a commercial civilian use round, making it more suitable for hunting applications, not unlike the 300 Blackout supersonic load.

In this regard we often see more soft point, hollow point and general use hunting rounds in 223 Remington as opposed to 5.56 NATO. However, 223 Remington is considered more of a small game or varmint round, as opposed to a heavier round like the 300 Blackout.

Again, it goes back to the purpose of the round and shows how a long range varmint round, as was the original intent of 223 Remington, cannot be justly compared to a slower, heavier bullet like the supersonic 300 Blackout. 223 Remington is ideal for coyotes and prairie dogs at long range whereas 300 Blackout is more suitable for deer or black bear at shorter ranges.

Shooting 300 Blackout Ammo with a Suppressor

As we mentioned numerous times by now, 300 Blackout has a subsonic range of ammunition choices and makes for an excellent suppressor host. The advantages are two-fold in that if one sticks to strictly subsonic loads they can shoot through a suppressor rated for 45 ACP or 9mm. Should the shooter wish to shoot the supersonic round suppressed, a silencer rated for 308 Winchester will easily handle both supersonic and subsonic loads.

300 Blackout subsonic is one of the quietest rounds to suppress, particularly when fired through a closed breech firearm like a bolt action or single shot rifle. There is no noise from the action or any created via the ejection process as noticed in a semi automatic firearm.

Additionally, we find 300 Blackout in supersonic form to have a very mild and pleasant tone when fired through most suppressors rated for 308 Winchester. It may not be as quiet as a 300 BLK subsonic, but sometimes absolute silence is not the goal.

Is 300 BLK good for Hunting?

The 300 BLK round is an excellent cartridge for hunting. Ballistically it performs similar to 7.62 x 39 or maybe the great American hunting round known as 30-30 Winchester or 30 WCF (Winchester Centerfire).

300 BLK has one distinct advantage over 30-30 Winchester in that 300 Blackout can use more effective Spitzer type bullets, where this is a rarity in most rifles chambered in 30-30 Winchester due to the use of a tubular magazine found on most lever action rifles chambered in 30-30 Winchester..

Likewise, 300 Blackout is a superior hunting round to 7.62 X39 because most 7.62 X 39mm ammunition is Berdan primed and steel cased and therefore non reloadable. Plus, 300 BLK has many more options with regard to bullet choices more suitable for hunting.

300 Blackout for Deer Hunting

Although it may not look like it at first glance, 300 BLK makes an excellent choice in a cartridge for deer hunting. There is a wide variety of factory ammunition and reloading components to make this an excellent short range deer slayer.

They key is to run the 300 BLK with supersonic loads and an appropriate projectile. This will allow for proper penetration and expansion and a marked level of improved performance when it comes to terminal ballistics. Simply put, the 220-grain subsonic loads will not give you that performance on a deer.

Another consideration is range – we find the 300 Blackout perfectly acceptable for taking deer within 150 yards. Performance is quite similar to the 30-30 Winchester, only we feel it is a more accurate round with much better projectile options for terminal ballistics on big game.

Closing Thoughts

300 Blackout is at the very least a very interesting and diverse cartridge for the shooter, hunter and especially a home reloader. Its dual purpose gives it a very distinct role in both personal defense and shooting sports. 300 Blackout seems to have become a mainstream round in the past decade alone, despite its origins in the 1990s in the form of the 300 Whisper wildcat type of round. As a subsonic suppressor host or as an intermediate hunting caliber, we expect to see 300 Blackout stay around for at least another half a century.