Two of the more popular calibers for AR-style rifle builds are 5.56 NATO and .300 Blackout.

They are also fairly similar calibers but quite distinct with respect to the relative advantages and disadvantages they offer.

So, whether you intend to build with a 5.56 or a .300 Blackout upper, here are a few things to know.

Why 5.56?

There are lots of reasons to love a build with a 5.56 upper and not so many not to.

For one, this has been the staple since the AR-15 was developed more than half a century ago. As a result, there are endless possibilities with respect to customizations and it’s very easy to find compatible replacement parts.

Then you can also consider performance. Both 5.56 and .223 are extremely accessible and affordable and popular throughout the whole country, so it should be relatively easy to find ammo.

In addition, 5.56 produces very little recoil, is lightweight and easy to handle, and shoots flat. This makes it a good cartridge for competition, including for long-range shooting.

It has practical and utilitarian uses too. The 5.56 NATO cartridge is excellent for most small to medium game, and it can be effectively used, with an appropriate bullet, for defensive applications as well.

With that said, there are distinct limitations of this cartridge. The main one is probably stopping power. For an intermediate cartridge, it’s very light and there are much more powerful cartridges out there.

This specifically brings up the practicality of a .300 Blackout upper as an alternative.

Why a .300 Blackout Upper?

Look at a .300 Blackout cartridge next to a 5.56 NATO cartridge and your first thought will likely be something like “they look basically the same, one just has a larger bullet.”

This is spot on, and in fact .300 Blackout cartridges are basically just necked out 5.56 casings with a larger, heavier bullet and a little less powder (which makes them highly economical for reloaders, by the way).

As a result, many parts that are compatible with 5.56 builds are also compatible with .300 Blackout uppers, minus, of course, the barrel and in some cases a few other parts.

That’s one reason to build with a .300 Blackout upper, but of course that begs the question, why even go through the effort? That’s easy; because of the close-range performance of the .300 Blackout cartridge.

The .300 Blackout delivers considerably greater stopping power at close range than the 5.56. This makes it better for defensive and sporting applications, and the .300 Blackout is also a popular cartridge for hogs and other intermediate game.

Also, because it uses less powder, it performs better from shorter barrels, which means that more compact builds can be made with it. Carbines perform well with .300 BLK as do short barrel rifles and even AR pistol builds.

There are two main caveats when it comes to choosing a .300 Blackout upper for your build. One is that this cartridge, despite its high close-range power, is abysmal at long range. The other is that, since this is a niche cartridge, it can be a bit hard to find and on top of that, it’s expensive even where you can find it.

But that doesn’t mean you shouldn’t choose it. You just need to match the upper to the application.

Where to Get Either?

Whether you ultimately decide to go with a 5.56 or .300 Blackout upper is up to you, but you can get either, and all of the rest of the parts you need for the project, over at MCS Gearup. Visit their website for more information and bookmark their page. If you tinker with guns a lot, you’ll need them sooner or later.

For more information about Micro Conversion Kits and Glock Kits Please visit: MCS Gearup.