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AR-15 Rifles Tactical

The Ultimate Urban Carbine Cartridge: 300 Blackout

by James Tarr   |  September 23rd, 2013 23

Over the last few months I have become a big fan of the 300 AAC Blackout cartridge (officially abbreviated 300 BLK). The primary reason for this is that for years I have believed we have been in need of a good carbine cartridge, a successor to the .30 M1 Carbine, and I think that the 300 AAC Blackout fits this need perfectly.

The .300-.221 wildcat cartridge (or .300 Fireball) has been around for quite some time, and was popularized most recently by J. D. Jones as the .300 Whisper. Jones took a .221 Fireball case (which has the same size base as the .223 Rem.) and necked it up to .300.

He was thinking more about the usefulness of the cartridge in suppressed AR-15s. Jones preferred to stuff big bullets into the little cases, favoring the 220-grain Sierra MatchKing bullets traveling downrange at about 1000 fps.

Remington recently introduced the .300 AAC Blackout cartridge. The dimensions of the two cartridges are identical, but the Whisper is still a “wildcat” cartridge. The Blackout has been SAAMI approved, which means that any ammo made or guns chambered in that caliber have to be made to certain dimensions and specifications. The Blackout tends to be loaded to higher pressures. While it is safe to shoot Whisper ammo in a Blackout-chambered rifle, the opposite is not always true.

Remington focused most of its effort on the Blackout’s capabilities for hunting and defense through the use of supersonic ammo. Much of the commercial ammunition made for the Whisper/Blackout features 110-grain bullets heading downrange at 2300+ fps. A .30 110-grain bullet? Why does that sound so familiar? Because it is that caliber and bullet weight combination you’ll find in the M1 Carbine.

The straight-walled .30 Carbine cartridge threw a 110-grain round-nose pistol-type bullet downrange at just under 2000 fps. Even as carbines go those are relatively anemic numbers, and while you will find a number of people who decry the carbine as being underpowered, you can find an equal number of people (including combat veterans) who loved it.

It was small, light, handy, held a lot of ammo, and was quick to reload when compared to the other shoulder arms of the day.

The Blackout, on the other hand, is pushing the same weight and diameter bullets over 300 feet-per-second faster, plus they are modern rifle projectiles, not downsized FMJ pistol slugs. Not only that, the cartridge was designed for the ubiquitous AR-15 platform. When it comes to performance and utility, I feel the 300 AAC Blackout is the modern evolution of the M1 Carbine cartridge, and that’s something we need.

AR-15s are everywhere. They are used for target shooting, competition, home defense, even hunting. Police department tactical teams have increasingly gravitated away from shotguns and HK MP5 submachine guns toward ARs as well.

But this is not necessarily a good thing. One size does not fit all.

The small, fast .223 bullet shoots flat at distance, but does that matter to anyone concerned about self-defense? Most defensive rifle shots taken by civilians or law enforcement will (and have been) taken at what most riflemen would consider “urban” or even point blank ranges, well inside 100 yards.

Pat Rogers, a retired Chief Warrant Officer of Marines and retired NYPD Sergeant with a wide and varied background in the CT Community, runs E.A.G. Tactical. For almost 20 years E.A.G. Tactical has been teaching military, police, and civilians how to win the fight.

“The majority of the carbine training we do is 50 yards and in,” Rogers stated. “This is for several reasons. One, it’s hard to find a range much longer than 50 yards nowadays, although occasionally I train military out to 300 yards. Second, whether you’re police or civilian, you’d be hard-pressed to justify a defensive shooting further away than that. Most of the police we see are using their carbines at pistol distances.”

I personally know a Detroit-area police officer who has been involved in four duty-related shootings. He used a carbine at pistol distances for all four.

Also, despite its popularity and the fact that our troops have been employing it against enemy combatants for the better part of 50 years, the round still has many detractors who say that a relatively small and light .22 bullet is particularly unsuited for anti-personnel use, much less barrier penetration.

Heck, the .223/5.56 is not legal for hunting anything other than small game in many parts of the country. When it comes to barrier penetration, mass beats velocity, and if there’s one thing you’ll find in an urban setting, it is things which do their best to stop bullets. Automobiles are amazing bullet traps.

For decades in this country the role currently occupied by the AR-15 was fulfilled by the M1 Carbine. I think we’re long overdue for a general purpose carbine round for the American citizen. Something that hits reasonably hard while still being soft shooting, can be used for hunting and self-defense at close to medium distance, and runs in an AR. I think the 300 AAC Blackout is that cartridge, and believe it is only fitting that a modernized M1 Carbine-type cartridge is now available for the AR platform.

The only thing required to change calibers to 300 BLK is a new barrel, although let’s be honest—most AR owners will just buy a second complete upper receiver/barrel assembly. There are many alternate-caliber AR variants. One advantage the 300 BLK has over them is that the ammunition, with only a few exceptions, feeds from standard GI MilSpec magazines.

As I write this there are no ARs to be found for sale anywhere due to panic buying, and magazines are either scarce or priced exorbitantly. The fact that 300 Blackout cartridges fit and feed from most standard AR magazines has now become a huge selling point.

So what does “most” magazines mean?

Traditionally, the .223/5/56 case neck indexes on the internal forward rib of the magazine. When firing Blackout rounds with shorter overall lengths (i.e. supersonic loads) the rib contacts the bullet on its ogive, and this usually isn’t a problem, especially when using modern magazines such as Lancer L5 AWMs or PMags, or GI magazines equipped with non-tilt (i.e. Magpul) followers.

Subsonic ammo for the Blackout is loaded with longer and, usually, thicker projectiles. With longer rounds, especially those with heavy bullets loaded to full mag length, the ribs tend to push the noses together and have the rounds interlace like fingers in the magazine. Depending on the gun/ammo/magazine, this may cause some reliability issues.

Prior to the panic buying of December 2012, Bill Alexander of Alexander Arms was working with D&H Magazines to produce a Blackout-specific magazine with a redesigned forward rib. He had just received some prototypes when everything went crazy, and now D&H (and everybody else who makes anything having to do with ARs) has been running as fast as they can just to stay in one place.

Whether we ever see Blackout-specific magazines now seems entirely dependent on what new legislation is enacted by those politicians who hate the very idea of guns.

With the 300 Blackout in mind as perhaps the ultimate urban defensive round for civilians (that includes law enforcement, for those of you ignorant of exactly what “civilian” means), I decided to put together an Ultimate Urban Carbine chambered in this relatively new cartridge.

If You Build It, They Will Come
Everything starts with the receiver, and I had a stripped lower receiver sitting around. “A lower is a lower is a lower” as Dave Fortier likes to tell me, and it’s true, to a certain extent. I had a standard lower receiver from a company now out of business, not one of the thick billet types, and it would serve my purposes just fine.

The first time I ever assembled an AR-15 receiver was when I was in high school. I had a stripped lower, a lower parts kit, and borrowed a buddy’s completed lower receiver so I could see what the finished product was supposed to look like.

For tools, I had a standard hammer, a vise, and some sort of oversized punch. I messed up putting the roll pin in for the bolt catch, so that the magazine followers never had quite enough oomph to lock the bolt back, but other than that was able to completely assemble my first lower back 25+ years ago without any instructions, just by eyeballing the finished product. Considering I have absolutely no mechanical skills, that says something about the simplicity of the AR-15 design.

This time around I had…Brownells.

Whatever you need when it comes to AR-15s, whether that’s parts or the tools to assemble them, Brownells carries it. The only downside to their vast selection is that it’s so…vast. Sometimes tracking down exactly what you need can take some work.

Wanting to do everything the right way, I remembered an email I’d received from Brownells not too long before spotlighting the free gunsmithing videos they have on their website, specifically videos about how to assemble an AR-15 lower receiver.

I know there are dozens of YouTube videos detailing how to assemble this or that, but considering they are of unknown provenance I wanted to do things right. I clicked on the green LEARN tab at and discovered…609 articles/videos covering gunsmithing of the AR-15/M4.

Trying to track down what I needed through the Brownells website wasn’t working as easily as I’d hoped, so I took a shortcut. I Googled “Brownells assembling lower receiver”, and that got me right to the page I needed.

There were seven videos explaining and demonstrating very simply how to assemble a lower receiver, and in no time I had a completed lower receiver assembly. I’d been wanting to try the new Magpul rubberized MOE+ grip, so I bought one of those and installed it on the lower.

I despise the standard heavy and gritty GI trigger pull. Unlike some projects I’ve been assigned, everything going into this gun was either already on hand, or bought with my own money. So, when it came time to decide what fire control system to put in it, I actually wanted to install a Geissele Super 3 Gun trigger, which is a single-stage design with a pull weight about 3.5 lbs. However, I didn’t have one on hand, and had no money to buy one. What I did have was the excellent Geissele SSA trigger, a two-stage design with a 4.5-lb trigger pull. In it went.

Step one done…now for the top end.

Embracing the urban environs/short range concept, I knew that shorter was better when it came to my project. One of the most fun guns I’ve had a chance to shoot this past year was the PDW in 300 BLK from Advanced Armament Corp (AAC themselves), which featured a 9-inch barrel tipped by a suppressor, for an overall length the same as a 16-inch barreled top end.

Most people, however, just don’t want to go through the hassle and federal paperwork required for an SBR (short barreled rifle) and sound suppressor. I decided a 16-inch top end would be the way to go.

Due to the big push from Remington/Freedom Group, finding companies making top ends chambered in 300 AAC Blackout was not difficult at all. While I had a nice top end from Wilson Combat on hand, I decided ultimately to go with an upper from Alexander Arms.

Alexander Arms has made a name for itself specializing in non-traditional calibers for ARs, specifically .50 Beowulf and 6.5 Grendel, but they recently began making ARs chambered in 5.56 NATO and 300 BLK.

My rifle had a 16-inch fluted stainless steel 1:8 twist barrel with a carbine-length gas system, their rifle-length Mk 10 handguards made of G10 composite, and was tipped with the very effective Blackout flash hider from Advanced Armament Corp.

I switched out the GI standard charging handle of the AA upper for a Gunfighter charging handle (Mod 4-Medium) from Bravo Company. Not only is the BCM version strengthened, but it features an oversize and serrated latch for secure manipulation. There are a number of companies who make oversize charging handles, but I haven’t found one yet better than the BCM.

The AA Mk10 handguards are modular, and accept rail sections just about wherever you want to screw them on. I installed two 2-inch rail sections at the front of the handguard, one to mount a front sight, the other at 9 o’clock to accept a sling mount and flashlight.

Any serious rifle should have back-up iron sights, and for this rifle I liberated a set from another rifle I had. The Bravo Company folding battle sights, made by Troy Industries, are as good as any sights out there, and better than most. As for an optic, considering I was putting together a carbine designed to be used at urban distances, any scope with magnification seemed a bit superfluous.

The EOTech Holosight has the red dot reticle against which all others are judged when it comes to speed and ease of use. There are lighter red dots, and red dots which provide a lot longer battery life (such as the Aimpoint Micro), but I’ve yet to find anything which can compare to the reticle and field of view of the EOTech. I had a relatively new EOTech XPS3 on hand, and slapped that on top of my receiver between the sights.

Slings are always a good idea, and I attached a VTAC (Viking Tactics) 2-point sling as well. I’ve played around with a lot of single-point and convertible slings, and I just haven’t found anything that is as useful as a good 2-point sling, and the VTAC, with its padded strap and quick adjustments, is as good as any sling out there.

In a box of spare parts in my basement I found a very cool and minimalist rail sling mount with QD sling socket which I attached at the front of the forend. I had no idea where I got it or who made it, and none of my gunwriter friends could ID it, so I went to the ultimate source—I keyword searched “rail sling mount” on the Brownells website and determined that it is the 10/2 Quick Detach Swivel Mount from Wilson Combat.

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