Yet another .300 Blackout disaster. Unfortunately, that .300 Blackout cartridge can fit in a .223 Rem chamber. Shooting a .308-caliber bullet in .223 bore is a recipe for disaster.
The .300 AAC Blackout aka “300 BLK”, is a compact 30-caliber cartridge designed to work in AR-15 rifles. It has a shorter cartridge case to accommodate the bigger 30-caliber bullet while still fitting in a standard AR-15 magazine. Unfortunately, that’s the danger. A careless shooter can toss a .300 Blackout cartridge in with .223 Rem rounds without noting. And because the case-head size is the same as the .223 Rem (5.56×45) the rifle’s bolt assembly will happily chamber and fire the .300 BLK round. Problem is, that forces a .308 diameter bullet down an undersized .223-caliber bore. Not good!
This images were provided by Tactical Rifle Shooters on Facebook. The message was clear: “Don’t try to run 300 Blackout in your .223/5.56mm. It won’t end well. The problem is identical rifles and identical magazines but different calibers.”
Image from Accurate Shooter Forum. Cutaway shows the jammed .30-Cal bullet:
For those who MUST have a .300 Blackout, here are some things you can do:
1. Use different colored magazines for .300 Blackout vs. .223 Rem.
2. Fit all your uppers with caliber-labeled ejection port covers.
3. Mark .223 Rem upper handguards with the caliber in bright paint.
4. Mark all .300 BLK Rounds with heavy black marker.
Comments by Folks Who Viewed these .300 Blackout Disaster Photos:
“The .300 Blackout is simply a badly-designed round. A properly-designed round would have had a feature in the shape that would have prevented cross loading in the first place.” — D. Santiago
“I almost made that mistake… I had a magazine of 300 BLK inserted in my .223/5.56 all night. Fortunately, I never pulled the trigger. Once I realized the mistake, I almost got ill. [After that incident] I no longer own a 300 BLK.” — B. Welch
“Happened to me hog hunting from a helo. Gun exploded in my face.” — B. Hood
“Fire-forming projectiles [is] so wrong in centerfire!” — M. Stres
“Had some dude come into the store the other day wanting .300 Blackout ammo to shoot in his 5.56 AR. It took 15 minutes of explaining for him to understand you got to have a .300 Blackout Upper!” — R. Williams
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Yet another .300 Blackout disaster. Unfortunately, that .300 Blackout cartridge can fit in a .223 Rem chamber. Shooting a .308-caliber bullet in .223 bore is a recipe for disaster.
The .300 AAC Blackout aka “300 BLK”, is a compact 30-caliber cartridge designed to work in AR-15 rifles. It has a shorter cartridge case to accommodate the bigger 30-caliber bullet while still fitting in a standard AR-15 magazine. Unfortunately, that’s the danger. A careless shooter can toss a .300 Blackout cartridge in with .223 Rem rounds without noting. And because the case-head size is the same as the .223 Rem (5.56×45) the rifle’s bolt assembly will happily chamber and fire the .300 BLK round. Problem is, that forces a .308 diameter bullet down an undersized .223-caliber bore. Not good!
This images were provided by Tactical Rifle Shooters on Facebook. The message was clear: “Don’t try to run 300 Blackout in your .223/5.56mm. It won’t end well. The problem is identical rifles and identical magazines but different calibers.”
Image from Accurate Shooter Forum. Cutaway shows the jammed .30-Cal bullet:
For those who MUST have a .300 Blackout, here are some things you can do:
1. Use different colored magazines for .300 Blackout vs. .223 Rem.
2. Fit all your uppers with caliber-labeled ejection port covers.
3. Mark .223 Rem upper handguards with the caliber in bright paint.
4. Mark all .300 BLK Rounds with heavy black marker.
Comments by Folks Who Viewed these .300 Blackout Disaster Photos:
“The .300 Blackout is simply a badly-designed round. A properly-designed round would have had a feature in the shape that would have prevented cross loading in the first place.” — D. Santiago
“I almost made that mistake… I had a magazine of 300 BLK inserted in my .223/5.56 all night. Fortunately, I never pulled the trigger. Once I realized the mistake, I almost got ill. [After that incident] I no longer own a 300 BLK.” — B. Welch
“Happened to me hog hunting from a helo. Gun exploded in my face.” — B. Hood
“Fire-forming projectiles [is] so wrong in centerfire!” — M. Stres
“Had some dude come into the store the other day wanting .300 Blackout ammo to shoot in his 5.56 AR. It took 15 minutes of explaining for him to understand you got to have a .300 Blackout Upper!” — R. Williams
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As the .30-Cal cartridge of choice for the AR15 platform, the 300 AAC Blackout, also known as 300 BLK, has become quite popular with black rifle owners. You can now purchase quality factory ammo and even premium Lapua 300 BLK brass. Some folks wonder — “why consider a 300 BLK”? Here are the key reasons you may want to acquire a 300 AAC Blackout upper for your AR:
FIVE REASONS to Shoot the 300 BLK:
1. Easy Conversion: Use your current AR lower, bolt/carrier, buffer, and magazine. The only part you need to change is the barrel. 2. Hunting Capability: 300 BLK conforms to state hunting regulations which may require a cartridge larger than .22 caliber. The 300 BLK shoots .308 caliber bullets. 3. Suppressor-Friendly: You can shoot heavier bullets subsonic. The subsonic capabilities of the 300 BLK make it ideal for use with a suppressed AR. 4. Great Barrel Life: With a .30-caliber bore and a modest powder charge, barrel life is outstanding. 5. Great Brass: No Case forming is required — just buy Lapua 300 BLK brass.
The 300 AAC Blackout was created by Advanced Armament Corp. and Remington primarily for the military as a way to shoot .30-caliber bullets from the M4/AR15 platform while using standard magazines. As explained by Robert Silvers, AAC’s R&D Director: “[You can] shoot 30 caliber from your AR while still using normal magazines with full capacity. Even the bolt stays the same, and all that changes is the barrel.” CLICK HERE for more information.
The concept of putting a .30-caliber bullet in a shortened 223 case has been done before, but not as an industry-wide standard that anyone can make products for, royalty-free. SAAMI, the industry standards organization, adopted and standardized the AAC 300 Blackout earlier this year. The SAAMI diagram for the 300 BLK is shown below.
Affordable Factory 300 BLK Ammo is Available
Remington now sells a variety of 300 BLK ammo: 1) 125 grain open-tip match with a custom Sierra bullet; 2) 220gr subsonic, and 3) 125gr AccuTip (photo below). While the 300 BLK is easy (and inexpensive) to reload, Remington and AAC recognized that most people are not reloaders. So Remington will be budget-priced UMC-brand 300 BLK ammo through at just $12.99 per box — that’s less than most other rifle cartridges than are more powerful than the .223.
The 300 AAC Blackout definitely works for hunters who want to use their AR15-platform rifle. And it also serves as a specialized 30-Cal “rule-beater” that lets 3-Gun competitors “make major” with a low-recoil cartridge that also offers long barrel life. For those who need to run a .30-caliber cartridge from a standard AR15 platform (as opposed to the AR10), the 300 AAC Blackout makes sense. But for hunters using a bolt gun, there are any number of tried and true options, such as the 7.62×39, .30-30, and, of course, the .308 Winchester (7.62×51 NATO).
WARNING: With some bullet options (and setback during chambering) 300 Blackout rounds will go into a .223 chamber and fire. Putting a .308-caliber bullet in a .224-diameter barrel is a recipe for disaster. You can blow up your gun and sustain serious injury. That’s why we recommend you have a dedicated 300 BLK upper and mark your magazines. Also, always, always check your .223 magazines to ensure no 300 BLK rounds worked their way in when you loaded the mags. There have been a number of Kabooms recorded from 300 BLK rounds fired in a .223 Rem/5.56×45 chamber. CLICK HERE to see actual 300 BLK in .223 Rem chamber.
The 300 AAC Blackout (300 BLK, or 7.62x35mm) was created by Advanced Armament Corp. and Remington in order to provide the military with a way to shoot .30-caliber bullets from the M4 carbines with only a barrel change. It has since become popular with AR shooters for a wide range of uses including hunting and home defense. With the increased popularity of this cartridge, folks have been looking for reliable 300 BLK load information. Now, thanks to Sierra Bullets, we have some good load data for the 300 AAC Blackout. Sierra has released a FREE 6-page Load Guide for this cartridge, as part of the Sierra Reloading Manual (5th Edition).
Here is ONE of SIX Pages in the Sierra Load Sheet for 300 AAC Blackout
About the 300 AAC Blackout (300 BLK)
The 300 AAC Blackout cartridge shares case-head dimensions and body taper with the .223 Remington. Not only does this allow for compatibility with existing magazines and bolts, but it allows reloaders to form their own brass from cut-down 5.56×45 mm or .223 Rem cases. You can also form 300 Blackout cases by necking-up .221 Fireball brass. Take Note: Lapua has started producing .221 Fireball brass — this should be available in the USA by early April.
The 300 AAC Blackout is a similar concept to previous wildcats, such as the 30-221 and 300 Fireball, as well as the proprietary 300 Whisper®, except that 300 BLK was the first to be a SAAMI-approved cartridge and any company is free to make firearms or ammunition.
300 AAC Blackout is also finding use with hunters, who may not have been able to legally hunt with .223 in their state, and who prefer .30 caliber bullets for medium-sized game. It provides similar effectiveness to the 7.62×39 or the slightly more powerful .30-30 cartridges except works in the more up-to-date AR-platform rifles. Effective hunting range is about 150 yards. Some innovators, such as Dave Whitford, have also experimented with the 300 BLK for Across-the-Course competition. READ Whitford story in Rifleman’s Journal..
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Sierra Bullets rolled out few new products for SHOT Show 2012. The one new bullet is a .30-caliber flat-based bullet, the 125gr OTM (open-tip match HP) MatchKing, item #2121. This unique flat-based bullet was designed in conjunction with AAC (Advanced Armament Corporation) and Remington for the new .300 AAC Blackout (BLK) cartridge, a relatively small cartridge based on the .223 Rem necked up to .30 caliber. The bullet length is tailored to correctly fit and feed from AR-15 platform magazines. The relatively light weight of Sierra’s new 125gr MK allows it to reach fairly impressive velocities even with a modest powder charge. Of course it can also be used in subsonic mode, running at sub-Mach velocities. However, it is more typical for .300 BLK shooters to run a heavier bullet, such as the 240gr SMK, for subsonic applications (the heavier projectile delivers much more downrange energy at subsonic MVs).
The projectile’s Open Tip is pinched for greater uniformity in the same manner as Sierra’s Palma Competition bullets. The G1 BC is surprisingly high for a relatively short, flat-based bullet: 0.310 (below 1600 fps), 0.330 (1,600-2,000 fps), 0.338 (2000 – 2650 fps), and 0.349 (above 2650 fps). Though it will perform well at low velocities in the .300 BLK, this bullet can handle the higher velocities produced by common .30 cal mid-sized cartridges, such as the .30-30.
The new 125gr Matchking is now being loaded in factory ammo, including Remington’s Premier Match, which retails for $34.00 for a 20rd box. These 125gr bullets are available now from MidwayUSA for $34.99 per hundred.
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Sierra has introduced a new .30-caliber flat-based bullet, the 125 grain OTM (open-tip match HP) MatchKing, item #2121. This unique flat-based bullet was designed in conjunction with AAC (Advanced Armament Corporation) and Remington for the new .300 AAC Blackout (BLK) cartridge. The bullet length is tailored to correctly fit and feed from AR-15 platform magazines. The projectile’s Open Tip is pinched for greater uniformity in the same manner as Sierra’s Palma Competition bullets. The G1 BC is surprisingly high for a relatively short, flat-based bullet: 0.310 (below 1600 fps), 0.330 (1,600-2,000 fps), 0.338 (2000 – 2650 fps), and 0.349 (above 2650 fps). Though it will perform well at low velocities in the .300 BLK, this bullet can handle the higher velocities produced by common .30 cal mid-sized cartridges, such as the .30-30.
The new 125gr Matchking is now being loaded in factory ammo, including Remington’s Premier Match, which retails for $34.00 for a 20rd box. These 125gr bullets are available now from MidwayUSA for $34.99 per hundred. Sierra offers five other bullets in the same general weight range that may work well in the .300 Whisper or .300 AAC Blackout:
.308 dia. 110 gr. FMJ Pro-Hunter Item 2105
.308 dia. 110 gr. HP Varminter Item 2110
.308 dia. 110 gr. RN Pro-Hunter Item 2100
.308 dia. 125 gr. SPT Pro-Hunter Item 2120
.308 dia. 135 gr. HPBT MatchKing Item 2123
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Smith & Wesson is going to produce an AR15-type rifle chambered for the .300 Whisper cartridge. This will be an addition to S&W’s Military & Police (M&P) Rifle series. As the first production rifle in the AR platform to be chambered in .300 Whisper (and .300 AAC Blackout), the new rifle offers both sub-sonic and supersonic capabilities. Originally developed and pioneered by J.D. Jones of SSK Industries, the 300 Whisper is based on the .221 Rem Fireball case necked up to .308. Notably, S&W says its M&P15 .300 Whisper is compatible with both the .300 Whisper and the .300 AAC Blackout (BLK) cartridges. The latter is a SAAMI-standardized, trademark-free variant of the .300 Whisper.
Manufactured on the M&P15 (AR-clone) platform, S&W’s new semi-automatic .300 Whisper rifle features an 1 in 7.5” twist, 16″ chrome-moly barrel. Both the forged 7075 aluminum upper and lower receivers have been coated with a Realtree APG camo finish. Standard features include forward assist and a six-position, collapsible CAR stock. MSRP for the complete rifle is $1,119. A separate .300 Whisper AR flat-top upper will also be offered, with an $819.00 MSRP.
“As the popularity of the modern sporting rifle continues to grow, more hunters are seeing the advantages of taking these firearms into the field,” said Mario Pasantes, S&W Senior Vice President of Marketing. “The M&P15 300 Whisper gives consumers the ability to use either lightweight or heavy cartridges during hunting or recreational applications without changing rifles or barrels.”
Is Hunting the Real Market for S&W’s .300 Whisper M&P15?
Editor’s Comment: If this gun is intended for hunting, we’re not sure Smith & Wesson got this one right. While the .300 Whisper is an interesting cartridge, it was originally designed to run sub-sonic, or be used with a suppressor. At sub-sonic velocities, the cartridge doesn’t pack much punch — not much more than a heavy pistol round. So you’re carrying around an 8-lb rifle (with optics) that only hits like a pistol. On the other hand, it can be loaded up to supersonic velocities, yielding ballistics similar to the .30-30.
But if you run it supersonic, why mess with this oddball cartridge at all? There are many other proven, game-killing chamberings for which a huge variety of inexpensive hunting ammo is widely available. (In fairness, .300 Whisper factory ammunition does exist. Hornady now offers both 1200 fps sub-sonic and 2375 fps supersonic .300 Whisper Ammo.)
Now the use of a .300 Whisper with a suppressor is intriguing. But, realistically, how many American hunters are going to get fingerprinted and pay the $200 tax for a suppressor, not to mention the hefty cost of the suppressor itself? As for the rifle configuration, a 16″ barrel is quite short for a hunting gun, and a wobbly first-gen collapsible stock that rattles is the last thing we’d want to take hunting.
Our guess is that most purchasers of this rifle will simply use it for plinking or tactical games, where the low recoil and long barrel life associated with the .300 Whisper will be welcome. One source suggests that the .300 Whisper has become popular with metallic silhouette shooters due to its low recoil and high accuracy. However we doubt you’ll be seeing many M&P15s on the silhouette course, given the funky, collapsible buttstock and short sight radius. (Under NRA Rules, AR15-type rifles are eligible for metallic silhouette competition under rule 3.1.2, but they must use “standard type stock[s]”.)
Story Tip by EdLongrange. We welcome reader submissions.
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The .300 AAC Blackout aka “300 BLK”, is a compact 30-caliber cartridge designed to work in AR-15 rifles. It has a shorter cartridge case to accommodate the bigger 30-caliber bullet while still fitting in a standard AR-15 magazine. Unfortunately, that’s the danger. A careless shooter can toss a .300 Blackout cartridge in with .223 Rem rounds without noting. And because the case-head size is the same as the .223 Rem (5.56×45) the rifle’s bolt assembly will happily chamber and fire the .300 BLK round. Problem is, that forces a .308 diameter bullet down an undersized .223-caliber bore. Not good!
The new 125gr Matchking is now being loaded in factory ammo, including Remington’s Premier Match, which retails for 
But if you run it supersonic, why mess with this oddball cartridge at all? There are many other proven, game-killing chamberings for which a huge variety of inexpensive hunting ammo is widely available. (In fairness, .300 Whisper factory ammunition does exist. Hornady now offers both 1200 fps sub-sonic and 2375 fps supersonic 
Our guess is that most purchasers of this rifle will simply use it for plinking or tactical games, where the low recoil and long barrel life associated with the .300 Whisper will be welcome. One source suggests that the .300 Whisper has become popular with metallic silhouette shooters due to its low recoil and high accuracy. However we doubt you’ll be seeing many M&P15s on the silhouette course, given the funky, collapsible buttstock and short sight radius. (Under 
