AR-15 Calibers: 5.56 vs .223
Your average AR-15 comes in two popular calibers, the 5.56x45mm NATO and the .223 Remington.
You can double-check what it is by looking at your model specs or physically on your barrel, which should be stamped with the caliber and barrel twist rate.
Faxon 16″ Pencil Barrel
The two cartridges are physically identical but the 5.56 may be loaded to higher pressures than .223 ammunition.
The .223 is a civilian round and has SAAMI specs (an organization that sets standards for pressure and dimensions) while the 5.56 is a military round that has their own specifications that might require higher pressure for higher velocity.
Therefore, it’s best to follow the advice:
- 5.56 chamber: OK to fire both 5.56 and .223
- .223 Wylde chamber: OK to fire both 5.56 and .223
- .223 Rem chamber: OK to fire only .223
Please note that .223 Rem and .223 Wylde are not the same things. One (Wylde) is perfectly safe to fire either 5.56 or .223, however, a .223 Rem chamber is not safe to fire 5.56 NATO.
Your barrel or rifle probably won’t instantly blow up from shooting a 5.56 in a .223, but why risk it?
Combine that with the variance in the machining of the barrel and ammo production standards, it’s best to use the proper ammunition.
The Rifle’s Heart and Soul
At the core of the rifle, resting comfortably and softly in the upper receiver is the bolt carrier group. The bolt carrier group is easily one of the most important parts of the rifle, and you have literally tons of options. If you want more specific info, check out our article on BCGs here.
However, if we are being legit with our A2 build we gotta go with the classic M16 full auto BCG, with a mil-spec phosphate coating. You have tons and tons of options, so the real question is which one do you want?
Personally, if I’m going legit A2 I’m going with a Colt BCG.
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It’s a little pricey, I know, but there are less expensive alternatives. Brownells, for example, makes a very simple and very affordable option.
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BARREL LENGTH
AR-15 barrels can be as short as 4 inches for blowback operated AR pistol builds up to as long as 24-inch rifle length barrels.
A 16-inch barrel is the required minimum length for rifles to not be designated as “Short Barreled Rifles” by the NFA, which require a $200 tax stamp to possess.
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An important consideration when it comes to barrel length is dwell time.
Dwell time is the time it takes for a bullet to exit the muzzle of a barrel after the primer has been hit.
As you pull the trigger, gasses start to propel the bullet down the barrel, where it acts sort of like a cork in a very long-necked bottle.
The gasses continue to expand, building the pressure behind the bullet as the space between the fired cartridge and bullet begins to grow within the bore.
The amount of pressure present behind that bullet is what determines the projectile’s velocity as it exits the muzzle of the rifle, being spun by the barrel’s rifling as it goes.
Because of this, bullet loadings perform better or worse depending on the length of the barrel. Too short, and the powder in the cartridge cannot be fully ignited to maximize the load’s velocity before the bullet has exited the barrel. Too long of a barrel, and the cartridge will completely burn its propellant before the bullet has exited the barrel. Take a look at our 5.56 and .223 Ammo here.
Shop Our 5.56 and .223 Ammo
So, when considering barrel length, it is very important to make sure you match your barrel with the type of ammunition you intend to shoot, while keeping in mind the performance you are looking to achieve.
Extras
Now the following items aren’t needed for an M16A2 clone, but they can add a little pizazz to your build. These accessories hark back to those easier days, where rails weren’t a thing, and our version of MLOK was duct tape.
The Marines have the essentials covered.
Bayonets
Bayonets are actually still issued with the M16A4 and the M4 rifles. Bayonets have been part of the military’s inventory for hundreds of years, and will likely remain so, but do you really need one?
Probably not, but a bayonet definitely adds something extra to the build. As much as I love things that go boom, I also like pointy things. I’m tossing two bayos up here because the M16A2 served long enough to be issued both.
Ontario M9 Bayonet
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The M9 bayonet is the bayonet of the United States Army. It doubles as a combat or general utility knife. A bayonet has to be extremely well made for it to function correctly. Good thing this bayonet is designed to be used as a spear point.
Ontario was one of the many companies who was contracted to produce the M9 bayonet and they still manufacture the design. If you’re buying a bayonet you might as well buy one from a company who makes it right.
Ontario OKC3S Bayonet
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This is the bayonet I know and love from my time with the Marines. The OKC3S is essentially the famous Marine Corps KA-BAR turned into a bayonet. It features a 7-inch blade with a little serration at the end. The OKC3S is issued to almost every Marine carrying a rifle and they were even used in Fallujah.
Marines still train with bayonets and are required to prove proficiency to obtain their tan belt and graduate boot camp.
Barska 4×20 Electro Sight
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This replica of the classic Colt scope proves you can toss an optic on an A2 without issue. Barska produces an affordable Colt replica that gives the user a 4 power magnification, and a sleek old school look. The Barska sight isn’t a go to war optic, but it’s perfect for capturing that old school cool look and feel of the A2 platform.
GI Sling
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In a day where elaborate slings rule the roost, the classic GI sling feels a bit underwhelming, but this style of sling has served for decades! It’s simple, reliable, and the M16A2 platform works perfectly with it. It’s another complete the look accessory.
TWIST RATE
Rifling in a barrel is spiraling grooves cut into the bore that twist at a rate along the length of the barrel. These rates of twist impart a degree of spin on a bullet as it is fired down the bore, stabalizing the bullet and improving accuracy.
Projectile weight primarily detmines what twist rate is required to properly stabilize the bullet.
Over- or under-stabilizing a particular bullet will result in a flight path that are undesirable and inaccurate.
Imagine a football flying with a perfect, tight spiral as opposed to wobbling off-axis. Thrown with the same velocity, one ball will be much more accurate and fly further.
Twist rate is read as a ratio, where the first number represents one complete rotation of the bullet and the second number represents the distance the bullet must travel down the barrel, in inches, to achieve one complete rotation.
For example, a common twist rate is 1:8. For these barrels, the bullet achieves one full rotation in 8-inches of barrel length.
Let’s cover how to select the proper twist rate for your application.
| AMMUNTION TYPE | WEIGHT IN GRAINS | OPTIMAL TWIST |
|---|---|---|
| .223/5.56 | 55 – 77 gr | 1:9; 1:7 1:8 |
| .224 Valkyrie | 75 gr. Plus | 1:7; 1:8 |
| 6.5mm | 120 – 140 gr. | 1:7; 1:8 1:9 |
| 300BLK | 110 – 125 gr. | 1:7 |
| 300BLK (Subsonic) | 200 gr. Plus | 1:8 |
| 7.62×39 | 122 – 124 gr. | 1:10, 1:9, 1:8 |
| .458 SOCOM | 500 gr. Plus | 1:14; 1:18 |
| .450 Bushmaster | 450 gr. | 1:24; 1:16 |
AR-15 Barrel Twist
Your barrel stamp should indicate the barrel twist after the caliber.
Criterion Barrels, Different Coatings
You should see a ratio of 1:7 all the way up to 1:12 and it means that the barrel will spin the bullet one revolution every X inches. Most barrels will be from 1:7 to 1:9 twist, with the most popular being 1:9.
Take a look at the chart below to see the ideal twist rate for your barrel.
Ideal Bullet Weight vs Twist, Shooters Log
The heavier grain bullets are usually reserved for the military and their tracer rounds.
With normal cartridges, you’re most likely to see 55 grain and 62 grain bullets. These are fine to shoot in 1:7 to 1:9 barrels and you probably won’t even notice a difference up to 300 yards.
Pistol Grips
There are two distinct mil-spec pistol grips used on AR-15 & M16 series rifles; the first one, used with the original AR-15 and all variants through the M16A1, is relatively smooth and has light checkering on the sides as well as a hole in the bottom-front of the grip that acts as a sling swivel mounting point (though was rarely if ever used in this fashion).
The second grip, introduced with the M16A2 and standard issue on all subsequent Colt rifles, adds a finger step between the middle and ring fingers, filled in the useless sling swivel hole at the bottom-front of the grip, has heavier checkering on the sides, and has ridging on the back for a better grip.
Original pistol grip on A1 lower
A2 pistol grip on A2 lower
Ручной пулемёт
Американская оружейная фирма Ares Defense Systems разработала в 1998 году семейство ручных пулемётов на базе AR-15 под названием Ares-16 в вариантах с комбинированным, ленточным и магазинным боепитанием под стандартный патрон 5,56×45 мм НАТО. Он был создан как попытка создать конверсионный комплект для переделки штатных автоматов М16 в вариант ручного пулемёта с ленточным питанием (оружие поддержки взвода, Squad Automatic Weapon в американской классификации). Верхний ресивер пулемёта совместим с нижними ресиверами (lower receiver) автоматов семейства AR-15. Вес оружия составляет 3,4 кг, что вдвое легче аналогичного FN Minimi.
Запирание канала ствола осуществляется поворотным затвором с 6 радиальными боевыми упорами, имеющими более прочную конструкцию по сравнению со штатным затворами автоматов AR-15. Газоотвод и поршень расположены слева от ствола, и при отделении ствола отсоединяются вместе с ним. Стволы быстросменные, воздушного охлаждения.
Центральным элементом системы Ares-16 является разработанная компанией Ares Defense Systems ствольная коробка с новой затворной группой и газоотводным механизмом. Механизмы оружия приводятся в действие газоотводной автоматикой с коротким ходом поршня. В базовом варианте все оружие линейки Ares-16 стреляет с закрытого затвора, автоматическим огнём и одиночными выстрелами, однако возможна переделка под стрельбу с открытого затвора путём установки соответствующего комплекта сменных деталей ударно-спускового механизма.
Gettin’ Low
That’ll about do it on our upper receiver so now we can focus on the lower half of your A2 build. The good news is choosing a lower receiver is pretty easy to do. Unlike an upper, you can basically use any standard mil-spec lower receiver.
The standard AR 15 lower receiver hasn’t changed since the A2 so you can throw a dart at the Brownells catalog and pick whichever receiver it lands on. Personally, I’m a fan of Spike’s lowers. They are well priced, easy to find, and high quality.
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However, any forged 7075 T6 aluminum lower with an anodized finish will be technically correct. Stay away from lowers with short throw safeties, and stay far away from polymer if you want a legit M16A2.
You’ll also need to put the clothes on (or in I guess) that stripped lower. For this, you again have dozens of choices. If we are keeping it legit you can go with the Colt Lower parts kit.
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This kit does not include the pistol grip or trigger. Both are easy enough to find.
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If you are looking to build an A2 for service rifle competition, then the Rock Island Match trigger is a great option for you. The Rock River Arms Match trigger provides a clean and crisp pull that comes in at about 4.5 to 5 pounds. It’s a two-stage trigger that is much cleaner and smoother than any mil-spec trigger.
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For those who want to go the simple route, there is are complete lower kits that are both affordable and easy to find. Bushmaster has a great classic mil-spec option that’ll fit in an A2 build.
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And for competitors that want to make their build easier, Rock River Arms also has a complete lower kit that includes their Match Trigger.
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If you want to make your build as simple as possible, there are always complete lowers with an installed lower parts kit. This will save you a bit of time, and likely some frustration from that irritating front pivot pin.
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The Unique Upper
What really sets the M16A2 apart from modern AR 15s is the carry handle equipped upper receiver. This carry handle upper receiver gives the M16A2 a very unique profile, and makes it stand out in a world of flat top uppers.
M16A2 Upper, note the carry handle.
This can be one of the harder parts to find, especially if you really want that classically fixed carry handle instead of a flat top with a mounted carry handle.
Detachable A2 Carry Handle – Aero Precision
Oddly enough I’ve never seen someone actually carry the gun by this handle. Personally, I know the idea of using the carry handle to carry the rifle would have resulted in ‘corrective action’ in boot camp.
The entire carry handle concept is odd, and I think that’s what makes the retro M16s so unique.
A Classic Example
Luckily, we have two options. One’s the classic choice, while the other is a more affordable option for those on a budget.
For a more authentic M26A2 clone, I suggest the Colt A2 upper receiver. This is as close to the actual military upper you are going to get your hands on.
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If you’re looking for something a bit less expensive, DPMS makes a very affordable and noteworthy model that’s true to the standard A2 design.
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The M16A2 upper is equipped with a robust rear iron sight with two apertures and tons of adjustment potential. The above uppers are both stripped, so you’ll need to purchase the rear sight separately.
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You’ll also need a standard upper parts kit to finish your rifle, including the dust cover and forward assist with the necessary springs and pins. Aero Precision makes excellent guns and gear, and this kit is a bargain.
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Best AR-15 Ammo
Now we combine the good stuff we learned above and stick to 55/62 grain bullets that are close to military specifications. These are the rounds that we’ve shot tons of and never had a problem.
Assorted 5.56 Rounds (XM193, XM855, Gold Medal 69gr)
Our suggestions are also all brass cased so you can keep them if you think you might ever start to reload your own ammo in the future.
1. American Eagle XM193
Our Editor’s Pick is currently American Eagle XM193 since it’s never failed to go *boom* and the price is almost always one of the lowest.
Best 5.56 XM193 55 gr
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Readers’ Ratings
4.97/5
(707)
2. PMC X-TAC XP193
Our second choice is PMC which also has never failed but is often a cent or two more than American Eagle.
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3. American Eagle XM855
Our favorite green tip ammo suggestion is going to sound about the same…what can I say, it works and the price is right.
Green Tip M855
Best 5.56 XM855 (Green Tip)
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4. PMC X-TAC XM855
And PMC’s X-TAC XM855 variant is also GTG.
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5. PMC Bronze
If your barrel is .223 or if you want to shoot some slightly lighter loads in your 5.56 barrel.
My personal favorite is PMC Bronze since it’s affordable and the brass is great for reloading. Plus…it’s on the low end of recoil so I love it for competition.
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6. Wolf Gold
If you aren’t looking to reload and want the best bang for the buck…all my buddies and I love Wolf Gold. Buy it cheap (1000 round boxes) and stack it deep! Wolf Gold is made in Taiwan and not Russia like other Wolf ammo.
Best .223 Bang-for-the-Buck
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And finally…if you’re going for pure accuracy…
7. Federal Gold Match 69gr
Our favorite when we do our accuracy testing.
Assorted 5.56 Rounds (XM193, XM855, Gold Medal 69gr)
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8. Tula & Wolf Polyformance
We don’t readily use these next suggestions in our AR’s, but if you’re really trying to save money, you can opt for Russian steel or coated steel cartridges.
Start off with a small batch first since some AR-15’s don’t like steel cased ammo. They offer pretty good savings but are dirtier shooting and less accurate…but probably great for the range.
Also keep in mind that you can’t save these to reload later, and you need to shoot at a range that allows both steel casings and bi-metal bullets.
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Self-Defense AR-15 Ammo
For self-defense you want the bullet to put all its energy into the bad guy by breaking apart.
That means FMJ and the penetrator rounds are usually not the best choice.
I recommend going with specific use self-defense ammo that is hollow/soft point and is used by law enforcement.
9. Hornady Critical Defense 55gr
Both Speer and Hornady are great but I give the edge to Hornady since I love their pistol defensive ammo.
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10. Speer Gold Dot Duty 55 gr
Another go-to brand for self-defense rounds…Gold Dot.
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That’ll Do For an A2
M16A2 builds, and retro builds in general, are a very popular trend in the AR world. Brownells is even selling old school AR receivers and furniture for A1s. Just a quick glance at R/guns reveals how popular retro builds are.
Plus you can get a full retro kit from Stag Arms.
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It’s odd to see so many people clamoring for carry handle equipped uppers, but I guess everything is cyclical.
If you need a more modern AR-15, you’ll want to read our Complete AR-15 Buyer’s Guide!
Readers, do you guys and gals have an interest in retro ARs? What about retro guns in general? Let us know in the comments!
Conclusion
That does it for BCGs…there’s lots to choose from…
Our Favorite BCGs
But if mil-spec is the name of the game…get the BCM.
Gold Standard Mil-Spec BCG
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If you’re looking for something mil-spec and a little upgraded with a Nitride coating…get the Rainier.
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To enter the lightweight BCG game…start with the Brownells Steel Lightweight. But be sure to get the most out of it with an Adjustable Gas Block.
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What kind of BCG do you run? There’s so many BCGs out there so let us know what we missed. And check out the rest of our Best AR-15 Upgrades.
Or…buy one!
Some of us love to pour time and money into our newest pet project, but not all of us actually have the time to finish it. It happens, we’re busy people! So if you don’t want to spend months parting out the perfect retro build – Brownells has your back.
Brownells has a complete like of AR-10 and AR-15 retro build parts and pre-made rifles ranging from the first generation AR-10s of 1955 to the CAR-15s of 1982. And these are some outstanding quality rifles!
Our favorite is the BRN-16A1 – a deeply faithful reproduction of the Army’s M16A1 that served in the jungles of Vietnam and across the world.
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Bullet Types
You’ll see two big families of bullet types, the full metal jackets (FMJ) and the hollowpoint/softpoints (HP/SP).
The FMJ’s are great for plinking while HP/SP are more for home defense or long-range applications. FMJ is also sometimes called Ball ammo.
Don’t you love multiple names for things…
Other confusing acronyms you might see include (BT) which means boat-tail and indicate the back of the bullet has a more aerodynamic shape than simply cutting off straight.
The middle one below is an FMJ-BT.
62gr XM855 vs 77gr SMK vs 55gr FMJ
Lastly, if you’re looking at military 5.56 rounds, you’ll see M193 and M855. The 55 grain M193 is the standard FMJ of the military while the 62 grain M855 is the “green tip” penetrator round that has a steel rod inside.
Assorted 5.56 Rounds (XM193, XM855, Gold Medal 69gr)
Things to keep in mind for M193 vs M855:
- Pricing is similar
- M855 is better at penetration (duh?)
- Some ranges do not allow steel core ammo like the M855
- M193 is better at soft targets under 100 yards
- More info about the differences
- Most of the time you’ll see XM instead of just M…that means it didn’t quite meet military specifications but still meets commercial specs. Learn more here.
