The next big thing in AR-15s may not be a piston driven operating system, or a fancy internal coating that requires little lubrication, or a new rail system for attaching accessories. The next big thing just might be the caliber that the AR-15 is shooting. The perceived issues with standard 5.56 NATO ammunition have led to the development of many competing “alternate” calibers for the AR-15 rifle. Calibers such as 6.8 SPC II and 6.5 Grendel promise better stopping power and increased effective range compared to the old 5.56. But I think the hottest new caliber of all is the .300 AAC Blackout, and here are a few reasons why:
1. .300 AAC Blackout is a .308 bullet inserted in a cut down 5.56 casing. The .308 caliber bullet may be the most common bullet diameter in the world, so this gives the .300 BLK unmatched selection in bullet types and easily available casings that can be quickly made with an inexpensive case trimmer and a cordless drill. This caliber is already super easy for handloaders, they can just trim 5.56 brass down to the correct length, create the .30 caliber shoulder with a resizing die, and insert their favorite brand of .308 bullet. Done! No waiting for another special run of bullets or casings to be made, and no paying high prices for specialized components. My friends and I make more .300 BLK brass every time we go shoot our 5.56 AR-15s—it just isn’t trimmed and sized to .300 BLK specifications yet!
2. Using 5.56 casings means standard magazines work and you get standard magazine capacity. 6.8 SPC II and 6.5 Grendel both require specific magazines different from each other and different from the Standard Nato Agreement (STANAG) AR-15 magazine. These magazines are not nearly as common, are not made by as many different manufacturers, and of course cost a bit more. On top of that, you lose capacity in those calibers, down to 25 rounds instead of 30, because their casings are fatter and take up more space inside the magazine. Barrett is the only manufacturer at this time making an extra-long 6.8 SPC magazine still holding 30 rounds. Since .300 BLK uses 5.56 casings, standard followers work just fine and capacity remains the same. Folks are shooting .300 BLK through Magpul Pmags and even Surefire 60 round mags with no problems at all.
3. The only difference between a .300 AAC AR-15 and a 5.56 AAC AR-15 is the barrel. Again, because 5.56 casings are used, you don’t need to swap out the bolt or buffer spring or anything else. Although buying another bolt isn’t a big deal for many shooters, bolts made with larger faces to accommodate bigger casings often have durability problems. 7.62×39 bolts in particular are notorious for always breaking at the same weak point. The AR-15 bolt was originally engineered with a certain amount of metal in the locking lug area for a good reason, and removing metal there to accommodate a larger rim weakens it. One solution is to just move to the much larger and heavier AR-10 platform—if you don’t mind lugging that heavy beast around. But anyone capable of swapping barrels on an AR-15 can convert their 5.56 NATO gun to .300 BLK with no additional changes. Of course, AAC, DS Arms, Black Dawn, and other companies offer complete uppers in the caliber—attach the upper to your lower receiver and you’re good to go.
4. Up close, .300 BLK hits hard. The supersonic loads for this caliber are more powerful than .30-30 or 7.62×39, and more accurate due to the .308’s more efficient bullet design. AAC claims that the .300 BLK is more accurate than 5.56 out to 300 meters, but that’s not the whole story. Chopping the carbine barrel down to submachine gun length is now the biggest trend in AR-15s for military, law enforcement, and even civilian shooters. It is well documented that the number of NFA applications to register short-barreled rifles with the BATFE has skyrocketed, and police and military buyers are looking for lightweight, handy carbines with barrel lengths in the 10-inch range. The problem is, 5.56 NATO loses a lot of its stopping power with a short barrel because it depends on velocity for terminal effectiveness. A 9-inch long .300 BLK barrel gives the AR-15 nearly 25% more muzzle energy than a 9-inch barrel shooting the 5.56. Even with a plain 16-inch long barrel, the .300 still features about 15% more muzzle energy than 5.56, but where this caliber really shines is when you’re shooting a short-barreled rifle. If you’re looking for a long-range caliber, 6.5 Grendel definitely has the edge, but most real world engagements with carbines take place within 300 yards, right in the wheelhouse of .300 BLK.
5. .300 is super quiet. Unlike 5.56, subsonic loadings that still cycle the AR-15s action reliably are easy to make. A 220 grain .308 bullet and a minimal amount of powder will result in a velocity of around 1000 feet per second. At close range, these 220 grain rounds really thump, and the real kicker is that using an AAC suppressor with them in a 9-inch barrel brings the sound level to only 125 decibels. That’s quieter than an MP5SD shooting 9mm rounds, and much quieter than a MK23 pistol shooting .45acp rounds. Statistics charts and YouTube videos don’t do it much justice—you have to be there and shoot one of these rifles with a “can” attached to realize that this 220 grain bullet is nearly as quiet as a silenced .22 pistol. For those of you who won’t ever get a supressor, this is a non-factor, but for folks who have discovered the joy of legally shooting quiet guns, the small powder charge and large bullet subsonic combination is tremendously exciting.
If you look at it one way, the .300 AAC Blackout gives you more stopping power than 5.56 NATO without having to change anything but the barrel on your AR-15. Put another way, you can have that extra stopping power in a package the size of a 9mm MP5SD, but even more quiet! Add in the fact that this caliber uses .308 bullets and reworked 5.56 NATO cases for maximum parts commonality, and you have a big stick that speaks very softly indeed. Daniel Defense, CMMG, Armalite, Bushmaster, Smith and Wesson, and Sig Sauer, and Wilson Combat are among the companies building complete rifles in .300 BLK now. Over 60 companies have announced that they are going to build product lines around the caliber. At SHOT Show 2012 it seemed like everyone was “jumping on the .300 BLK bandwagon.” AAC’s .300 BLK “Honey Badger” PDW concept has early adopters clamoring for more. Right now it looks like .300 BLK is 2012′s most popular new caliber, and the next big thing in AR-15s.