.308 vs 5.56: A Caliber Comparison
Few cartridge showdowns are bigger than the comparison between the cruiserweight .308 Winchester (aka the 7.62x51 NATO) and the scrappy bantamweight 5.56x45 NATO. Both have a strong military pedigree, both are combat proven, and both have legions of loyal fans. Though often viewed through a lens of “which is better?” these cartridges have served alongside each other in different roles for several decades now. Let’s take a closer look at these rounds and see where they came from and what, if any is better about one versus the other.
A Brief History of .308
The .308 Winchester (we’ll just call it the .308 from here on out) was designed in 1952. Just a few years prior the US and the Allies had won WWII. The US’s battle rifle, the M1 Garand had served admirably (and would serve admirably in Korea, as well) but a replacement was being sought. Not only was a replacement rifle being sought, but so was a replacement cartridge. This cartridge would also become the standard battle rifle round of the North Atlantic Treaty Organization (NATO), hence the cartridge’s designation.
A newer NATO cartridge would be smaller. Smaller equaled lighter weight, the ability of the soldier to carry more ammo, and a smaller, lighter delivery platform. The result was the .308 Winchester, essentially a shortened .30-06 Springfield. Three early military rifles were designed around the .308: the US’s M14 from Springfield, the FAL designed by Fabrique National in Belgium, and the G3 from Germany’s Heckler and Koch.
All three of these rifles would serve in their respective military’s hands for decades to come and all would develop loyal and devoted followings. The “battle rifle” concept didn’t last long, however. The US Army ditched the battle rifle in Vietnam due to its weight and unwieldy length. The M14 has the ignoble distinction of being the last main battle rifle issued by the United States, as well as being one of the shortest-lived general issue rifles in US inventory.
The .308 didn’t go away, however. Instead, it was chambered in the machine gun that replaced the .30-06 caliber machine guns of WWII: the M60. The M60 general-purpose machine gun (GPMG) would become iconic in its own right. It was eventually replaced with FN’s M240 machine gun, also in .308, and various sniper rifles in US inventory are chambered in .308, as well, including the M110. The .308 wasn’t confined to military applications; indeed, it has been incredibly popular on the civilian market since its inception.
A Brief History of 5.56
The .223 Remington came along in 1962, a decade after the birth of the .308 Winchester. The little cartridge was designed as a deliberate project for a high-velocity, lightweight bullet for military use. It would eventually be chambered in Eugene Stoner’s brainchild, the M16 and the civilian version, the AR15, that we all enjoy today.
As we have seen, the .308 and its platform, the M14 were less than ideally suited for the jungles of Vietnam. A number of factors played a role in its replacement including size and weight, and the fact that the M14s wooden furniture would swell in the jungle heat and moisture causing erratic zero shifts. These factors, doubtlessly combined with others, led the US to adopt the M16 and its very lightweight 5.56 cartridge for general issue.
The .223 Remington was improved and by the early 1980s was designated the 5.56x45mm NATO, a high-pressure version that was not backward compatible with .223 chambers. Though the adoption of a small-caliber combat rifle was somewhat controversial at the time and in the post-Vietnam years, we now know that the 5.56 is quite the capable combat chambering. It – and its parent platform, the AR – have proven themselves reliable and lethal.
The 5.56 has expanded far beyond the AR15. It is also the chambering of the M249 Squad Automatic Weapon (SAW) and a host of other light machine guns. It can be had in bolt action rifles, as well. The 5.56 is probably the most popular rifle cartridge on the civilian market today.
308 vs 5.56 - Let’s look at the differences between these two cartridges.
Cartridge Specs: First, the .308 is a much larger cartridge than the 5.56. The .308 has an overall length of 2.80 inches, while the 5.56 has an overall length of 2.26 inches. This means that the .308 requires a longer action (and hence, a larger and heavier gun) to function. The bullet diameter of the .308 is, well, .308 inches. This is quite a bit larger than the .224-inch bullet of the 5.56. Typical bullet weights for the .308 are 150, 165 and 180 grains, while the 5.56 fires much lighter bullets in typical weights of 55-, 62, and 77 grains. Combined with a heavier bullet the .308 is the clear winner in terms of sheer power.
Recoil: This power comes at a cost. Recoil is night and day between these two rounds. While neither is punishing, the .308 generates much more recoil than the 5.56. This can be problematic in some circumstances, like full-auto fire. As the military learned, full auto fire of a .308 battle rifle is a losing proposition. This also comes into play in close quarters where fast target transitions are very important.
Velocity & Energy: The muzzle velocities of the two cartridges is different, but not as much as one might expect. Fired from a 24” barrel, a 150-grain .308 bullet is expected to achieve a velocity of around 2,800 feet per second. This generates a very impressive 2,600 ft-lbs of muzzle energy. Compare that to the lightweight 5.56. Fired from a 20-inch barrel, a 62-grain bullet should reach approximately 3,100 feet per second, generating only half the muzzle energy of the .308 at around 1,300 ft-lbs. That’s a pretty big difference and the .308 has a clear advantage in terms of energy.
Trajectory: How does that translate to bullet trajectory, though? Let’s take a look at the two cartridges’ performance at distance. Again, using a 150-grain .308 bullet fired at a muzzle velocity of 2,800 feet per second, bullet drop at 500 yards is just a hair over 54”. Let’s compare that with the same 62-grain 5.56 bullet fired at 3,100 feet per second from the muzzle. It has a bullet drop just a shade under 47 inches at 500 yards. This does give the 5.56 a slightly flatter trajectory but at such distance its energy is fading fast, while the .308 still has power to spare, it a longer effective range.
Sectional Density: Sectional density is the combination of a bullet’s surface area and its weight. Combined these two factors predict how well a bullet will penetrate on a target; the higher the number the more the bullet is expected to penetrate. This gives us some indicator of a bullet’s terminal performance. The 150-grain .308 is a larger bullet with more surface area, but with much more weight behind it than the 5.56. The sectional density of the .308 is .226 while the 62-grain 5.56’s sectional density is only 0.177.
Both the .308 and the 5.56 are very popular rifle cartridges for civilian, law enforcement, and military use. Both have a broad set of applications. Let’s take a look at possible uses for both of the chamberings.
With full metal jacket bullets both are marginal performers on game but with modern, expanding soft points, both are amply capable hunting rounds. The .308 is preferred for large game, longer distances, and can take just about anything on the North American Continent. The 5.56 is capable of taking game up with whitetail deer, as well as smaller game like varmints. Both are also great choices for self-defense and law enforcement applications. The 5.56 is preferred in close quarters due to less recoil, while the bigger .308 is the go-to for greater distances.
.308 and 5.56 Upgrades from SOTA Arms
Both the .308 and 5.56 are right at home in semi-automatic rifles. The biggest difference – the size of the cartridge, bullet, and gun that fires it – should guide your decision in which to choose. Once you’ve decided, SOTA Arms has what you need to start, and finish, your next AR build.
.308 ARs: If you want an AR in .308 you will have to invest in a new lower receiver, as well. The longer cartridge requires a longer magazine well, and this platform is known as the AR10. SOTA Arms offers complete lowers, stripped lowers, an 80% lower, and all the parts you need to assemble a lower receiver. We also offer complete AR10 upper receiver assemblies in 18-inch and 20-inch barrel lengths, as well as a host of other AR10 parts like bolt carrier groups and magazines.
5.56 ARs: Of course, we also offer a broad selection of AR15 rifles chambered in the venerable 5.56 cartridge. Our “Guns of Color” line offers an extensive selection of complete rifles, and mated, stripped upper and lower receivers for those interested in a DIY build. We also have all the upper receiver parts you need including bolt carrier groups, gas blocks, handguards, and the upper receivers themselves.
Check out our inventory of ar-15 complete uppers!
Optics are an important part of a modern weapons system. Once derided as too fragile for general use, the last couple of decades in Iraq and Afghanistan have taught us that optics can survive day-to-day use and abuse. Even the Marine Corps, long enamored with iron sights, has seen the value of magnified optics and now provides them as a general issue item.
Magnified optics (aka “scopes’) are now on AR-15 rifles of all types. From long-range precision rifles to hunting rifles to do-it-all, multi-purpose guns…even CQB-oriented rifles are now sometimes equipped with low-powered variable optics (LPVO). A scope can increase your hit potential by upping your accuracy. A scope can also make it easier to observe the target – a good thing whether you are a tactical shooter or hunter.
All of SOTA Arms’ AR-15s are equipped with a flattop upper for ease of mounting an optic. Mounting a scope can be a little tricky, though. Today we are going to take a look at mounting a scope, including choosing your scope and mount, what tools you need, and the actual mounting. Let’s get into it!
Types of Scopes and Mounts
It should probably go without saying, but before you begin mounting your rifle scope you will obviously want to choose your scope. The rifle’s application will have a lot to do with that; it wouldn’t make much sense to put a 12-power scope with a huge objective lens on a 10.5” AR pistol. It also probably wouldn’t be fitting to put an LPVO on a 24-inch varmint rifle. It’s up to you to know your rifle’s purpose and choose a scope accordingly, but there is a quick rundown of the most common types of scopes.
Red Dot Optics: Though not actually telescoping and not technically “scopes,” this is perhaps the most common type of optic for AR-15 rifles. These optics are 1-power or zero magnification and are meant for fast, close-in work. Mounting these is simple as they already have a built-in mounting base that attaches to a Picatinny rail.
Uses for Red Dots: Home defense rifles, CQB carbines, short-range hunting.
Low-Powered Variable Optics (LPVO): This type of optic typically has a very low magnification setting, typically 1x (zero magnification) or 1.5x for fast, close work, and features rapidly changeable magnification up to about 4x or 6x. These scopes are incredibly versatile and are rapidly gaining popularity as the tactical scope du jour. The LPVO offers maximum versatility.
Uses for LPVO: Patrol rifles, do-it-all rifles, brush guns, and general-purpose tactical rifles.
Traditional Riflescopes: Traditional riflescopes come in either fixed or variable power and usually offer higher magnification. Variable-power scopes are very popular today, on everything from ARs to bolt-action rifles, with 3x-9x being the typical range of magnification. These do have the disadvantage of larger lenses, meaning they must be mounted higher above the rifle’s bore.
Uses for Traditional Riflescopes: Hunting, long-range target shooting, tactical marksmen.
Your purpose for having a scope will largely dictate the type of scope you choose. Another guiding factor will be the cost, but there are options ranging from affordable to top-of-the-line in all of these categories. There are also several other categories of niche scopes, but these are the mainstays.
Types of Mounts
Since you can’t mount a scope without mounts, let’s look at them too. The different types of optics mentioned above take different types of mounts. You don’t have to go all-out pricewise to get a decent mount, but you should buy quality; if your scope isn’t securely mounted your accuracy will suffer. As mentioned, most red-dot optics have a built-in mount and nothing more is required.
LPVO optics often mount in what is known as a “one piece” mount. These mounts consist of a solid, one-piece base that includes the bottom halves of the scope rings built in. The basic steps to using a one-piece mount are to first mount it to the rifle’s rail and remove the top rings. Then scope is set in the bottom piece, and the top halves of the rings are placed over it and tightened, securing the optic. One-piece mounts range in price from $50 to close to ten times that.
Traditional riflescopes usually mount in scope rings. These are rings that clamp around the scope, one near the objective lens, and one near the ocular lens (the lens closest to the shooter’s eye). Scope rings are typically two-piece affairs with a bottom portion that mounts to the gun’s rail or scope mount, and a top portion that secures the scope. One important factor when choosing scope rings is the diameter of the scope’s tube. This number is usually expressed in millimeters with 30mm and 40mm tubes being very common. Make sure you choose rings that match your scope.
Tools You Need for Scope Mounting
You will need some tools to mount your scope. Having the right tools will make the mounting process go much more smoothly.
· Gun Vice: You need something to hold your AR platform during the mounting process. It should be stable, and it should hold the gun level.
· Torque Wrench: you need to tighten screws to fairly precise in-lb measurements, not just “finger tight.”
· Bubble Level: if your scope is not level your adjustments won’t correlate to real-world impact. A level is necessary to level your scope so that the reticle is a truly vertical line bisected by a truly horizontal line.
· Thread Locker for locking screws in place.
How to Mount a Scope
Mounting a scope isn’t all that difficult, but it does require time, focus, and patience. Take your time, use quality components, and use the right tool for the job. This makes your optic and mount live up to the SOTA Arms AR-15 they are mounted on.
SOTA Arms AR15s are some of the best in the industry. Each one of our rifles – from our Guns of Color in 5.56 to our complete upper units in calibers from 6.8 Grendel to .300 Blackout to 7.62x39 to .458 SOCOM are all built with precision and top-quality parts. Each rifle and upper is built quality you can bet your life on.
Find the best scope for your ar-15 in our shop today!
Custom AR-15 made in honor of my dad
SOTA Staff Stories:
In Honor of my dad
When I take one rifle out of my gun safe, it brings smiles to my face every time for so many reasons. This rifle was made in honor of my dad, he enjoyed the sport and grew up with his dad enjoying rifles. He had a great collection and then started collecting handguns. My dad unfortunately passed away a few years ago but before he passed away, he had one final wish for me and that was that I would get my conceal and carry permit. He said he wanted me to learn to protect myself and I think he secretly knew I would enjoy the sport. I decided to build my first AR but in doing so I wanted to honor him. I had his name and dates engraved on a Sota Arms lower receiver. I really wanted to make this rifle something I would love and something he would be proud of. Now I get really excited to take my rifle out and shoot it at the range.
Jen S, Customer Relations SOTA Arms