5D Tactical

For those of you thinking about creating your own AR platform with a receiver blank, a jig, and a build kit, you’re going to have to give some serious thought to cartridge pairing. Do you want to complete your build with a 5.56 complete upper, which for a long time has served as the “standard” for AR-15s, or are you interested in completing your build around another cartridge, like the .300 AAC Blackout?

Let’s take a closer look at each of these cartridges.

5.56mm NATO

The 5.56mm NATO cartridge was developed over half a century ago as an alternative to the heavier 7.62mm NATO cartridge. It quickly became very popular and has enjoyed wide popularity ever since.

Quick 5.56mm NATO Specs:

  • Overall length: 57.0mm
  • Case length: 44.7mm
  • Bullet diameter: 5.7mm

Bullet weight, obviously can vary significantly, as can ballistic performance, in response to the specifications of the load. However, 55-grain bullets are very common for 5.56 NATO loads, as are 62 and 63-grain bullets.

Although the load is subject to change, 2,500+ FPS muzzle velocities are common with 55 grain bullets, which also commonly generate over 800 ft/lbs of force at the muzzle. Ballistic performance drops steadily with range; at 500 yards, the same load would carry just over 200 ft/lbs.

.300 AAC Blackout

Now let’s consider the .300 AAC Blackout, which was interestingly enough developed to replicate the performance of the 7.62x39mm. The idea was to create a cartridge that was compatible with similar rifle platforms and offered greater stopping power.

The parent case of the .300 AAC Blackout is actually the .223 Remington, which is equally interesting. It’s cut down and necked out to accept larger, heavier bullets that can feed from AR magazines.

Quick .300 AAC Blackout Specs

  • Overall length: 57.0mm
  • Case length: 34.7mm
  • Bullet diameter: 7.8mm

As you can see, the overall cartridge length of the two is identical; the case is shorter so it can accept larger, wider bullets. They are correspondingly heavier, with common standard weights of 78, 110, and 125 grains.

As with any cartridge, ballistic performance is going to vary according to the load. Just to offer a frame of reference, a factory loaded.300 AAC blackout cartridge with a 110-grain projectile fired from a 16” barrel can produce muzzle velocities of over 2,300 FPS and over 1,400 ft/lbs of force.

Though the muzzle velocity generated by the .300 AAC Blackout is lower than the 5.56, the heavier projectiles will engender two specific, important traits. One is that the trajectory will droop noticeably beyond 100 yards. The other is that the projectile carries energy, often more than double that carried by a 5.56 round open impact past 100 yards.

Closing Thoughts

Volumes more could be written comparing the ballistic performance of these two cartridges (and they have been) but if you’re looking for a really brief synopsis, here’s the takeaway:

  • 5.56 NATO shoots faster and fatter than .300 AAC Blackout but loses ballistic energy more rapidly.
  • .300 AAC Blackout doesn’t have the same muzzle velocity and droops significantly past 100 yards but carries ballistic energy effectively.

Whichever you choose to construct your home build around, get your .300 AAC Blackout or 5.56 complete upper receivers at 5D Tactical at 5DTactical.com. In addition to .300 AAC Blackout and 5.56 upper receiver assemblies, 5D Tactical sells 80% lowers, 80% lower jigs, and build kits – everything you could possibly need to complete your home build, from butt to muzzle, including upper assemblies, charging handles and everything in between.

Visit their website at 5DTactical.com or contact them directly at Sales@5DTactical.com or by phone at 508-834-4223.

For More Information About 308 Upper and Billet 80 Lower Visit 5D Tactical.

By Adam

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