The 5.56x45mm NATO cartridge was initially adopted in 1963 as a replacement for the 7.62, which was heavier, bulkier, and produced more recoil.
The lighter kicking 5.56 delivered similar ballistic performance but was more compact, lighter, more affordable, and, well, you’ll see all the virtues of this cartridge if you read the article.
Here are all the best reasons to build an AR-style rifle with a 5.56 upper.
1. Compatibility and availability of parts
Since the 5.56 cartridge has been in official use for basically 60 years, the market is awash with products, both parts and accessories, official issue, new, and surplus, that are compatible with 5.56 AR platforms.
Whether you’re looking for a new barrel, muzzle device, BCG, stock, grip, or even a 5.56/.223 mag, it’s not more than a few clicks away or a short trip to the gun shop. Many M16 parts can even be used with AR builds.
2. Easier to control under rapid fire
One of the main reasons that the 5.56 was initially developed was that the 7.62x51mm NATO cartridge, in the M14 rifle, was difficult to control under rapid fire. It just kicked too hard. A 5.56 rifle is much easier to control under full-auto fire (or rapid semi-auto fire) than other, heavier alternatives like .308 or .30-06.
3. Great for high–volume target shooting
Given its price, size, performance, and low recoil, the 5.56 round is a great one for high-volume target shooting, whether you’re out there for fun, range therapy, or even competition. It also makes a great training round for these reasons.
4. Low cost of entry
Because parts for rifles built around these cartridges, as well as the cartridge itself, are so widely available, prices are pretty reasonable. It’s a lot more economical to build a rifle with a 5.56 upper than one with a niche chambering, like .50 Beowulf.
5. It’s an extremely versatile round
There’s really not a lot you can’t do with a 5.56 rifle. You can use it for hunting, training, target shooting, plinking, long-range shooting, defensive applications, and more. It’s like the ultimate, short-action, low-cost centerfire caliber.
6. There’s basically no recoil
The 5.56x45mm NATO produces some of the lowest free recoil of all centerfire rifle cartridges. Most rounds will produce muzzle energy in the neighborhood of 1,300 ft-lbs or so.
From a smooth-shooting rifle with a gas-impingement system, recoil is basically nil. Install a muzzle brake and you won’t even feel it.
7. Suitable for small and medium game as well as predators
Even though this is a small cartridge, it’s king of the pack for use against predators like coyotes and foxes, as well as varmints like prairie dogs. You can even take medium-sized game like whitetail deer (where legal) with a round like this.
8. It’s a good round for long-range competition
The 5.56x45mm NATO cartridge is also excellent for long-range competition. There are hotter, faster, flatter-shooting rounds, but these will burn out barrels faster.
A rifle with a 5.56 upper will enjoy longer barrel life, and bullet drop is not that bad. It drops ever so slightly faster than .223 (which is loaded to lower chamber pressures), falling about 1.75” at 100 yards, down to about 54” at 500 yards. This is a relatively flat trajectory that is suitable for long-range competition with, say, a 200-yard zero.
9. It has defensive applications
There are better cartridges for short-range engagements, especially from basically the same rifle - like .300 Blackout - but 5.56 is still a great option for close-range defensive applications. There’s a risk of over penetration with a fast, light cartridge like this, though, so if that’s your aim, make sure you use soft-point or hollow point bullets.
10. It’s cheap
The 5.56 NATO is one of the most affordable centerfire cartridges in the industry, hands down, with prices usually ranging between 50 cents and a dollar per round. Also, you can get bulk and surplus deals, driving down per-round costs even more.
11. It’s available
Because it is widely used in official service, there’s really never a shortage of 5.56 NATO ammo. Other cartridges might be hard to find in this ammo crisis, but typically not this one.
12. You can find bulk deals
If you shop around (or check online retailers) you can usually get bulk deals on 5.56 ammo which can make it even more affordable than it already is.
13. It’s light, making it easier to carry
This cartridge is lighter and more compact than other centerfire cartridges like 7.62x51mm (or .308) or even .30-06. As far as rifle cartridges go, it’s about as compact as they come, and light. This is great for hunters that still hunt and cover a lot of ground chasing game, rather than hunting from a blind.
14. You can pack more rounds into a tight space
Not that it’s a huge deal, but you can carry more 5.56 rounds in a small space, or pack more mags, than you’d be able to do with a heavier, larger cartridge.
15. Minimal muzzle flip
Not only does 5.56 produce minimal recoil, but it produces really little muzzle flip. This enables faster, more accurate follow-up shots than you’d be able to make with a heavier, harder-kicking cartridge.
Install a muzzle brake and muzzle flip will diminish even more.
16. It’s accurate
While some will tell you that 5.56 is not inherently as accurate as .223 (there’s .223 Wylde for that), it’s still a fairly accurate round. Go with a shorter barrel if you’re shooting or hunting at longer ranges with 5.56, which may improve accuracy slightly.
17. Good for training beginners
Because 5.56 produces little recoil, it’s a great centerfire cartridge for training beginners. The .22LR might be better, but then you miss out on most of the other advantages mentioned here.
18. You can still use it with .223 Remington
While you should only ever fire the rifle with the ammo that’s indicated expressly as printed on the barrel stamp, you can probably safely shoot .223 Remington through a rifle with a 5.56 upper. Just make sure you don’t reverse that. They’re one way compatible, and you can’t shoot 5.56 through a .223.
5.56 Uppers Are Here
These are just some of the best reasons to build an AR with a 5.56 upper. We have all the other parts you’ll need as well, including parts kits and complete AR build kits.
Get started here and contact us at Sales@MCSGearup.com if you have any questions.