.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!
AR-15 80% LOWERS
Browse our selection of lower receivers for AR 15, AR 10, and 9mm. We offer stripped lowers, complete lower assemblies, and partial lower assemblies. Each lower features a Magpul-style trigger that has been machined in and is designed to fit Mil-spec uppers. All of our lowers are machined in house in our Minnesota facility, from billet aluminum, and given a hardcoat black anodized for superior quality, durability, and performance. Whether you are looking for a AR 15 lower receiver, a AR 10 lower receiver, a 9mm lower receiver, or lower parts, SOTA Arms will set you up for success!
Custom AR-15 lowers designs
When ordering these special lowers please leave us a note with the person's name, dates and if you would like the lower black anodized and or white raw. (This note can be placed in the shipping address if different) We will also need the name of your FFL.
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The AR15 platform is perhaps the most versatile rifle in existence. Not only does this include an ever-expanding line of external parts and accessories including stocks, forends, optics, lights, and other paraphernalia, the very cartridge around which the rifle is based is variable. Hunters, soldiers, competitors, and tinkerers are always looking to improve on the ballistics of the platform.
Two such improved cartridges are the closely related 6.5 Grendel and 6.8 SPC. These cartridges have a lot in common, and both deliver a heavier bullet than the 5.56, resulting in over 40% more energy to the target. But is one better for you? This article will explore the differences between the two.
A Brief History of 6.5 Grendel and the 6.8 SPC
The 6.5 Grendel cartridge is one such attempt to elevate America's Rifle. The Grendel was unveiled in 2003, the brainchild of Bill Alexander (who can also lay claim to the .50 Beowulf). Ballistics were intended to best the 5.56x45 NATO, and they easily did so. In fact, the early 6.5 offerings gave the .308 Winchester a run for its money, shooting flatter and staying supersonic longer. All this while still fitting in a standard AR15 platform and utilizing a STANAG magazine. Since its SAAMI standardization in 2010, it has become one of the top "alternative" AR chamberings.
Meanwhile, from 2002-2004 the 6.8 Remington Special Purpose Cartridge (SPC) was under development. Rather than a visionary wildcatter, this cartridge was designed by Remington Arms with input from the Army Marksmanship Unit and the U.S. Special Operations Command (USSOCOM). It was designed to address failings of the 5.56 cartridge out of shorter-barreled M4 carbines while still operating in the same-sized platform and legitimized by SAAMI in 2004. The cartridge reportedly performed well at close range but was shelved by the military for a variety of reasons.
While neither cartridge was adopted in any significant numbers by the military, they weren't forgotten, either. Both hung on and both are perhaps more popular today than they were ten years ago. For the record, neither intermediate cartridge is confined to the AR-15 platform, and both would make fine short-action bolt-action cartridges, too. Let's take a look at these two cartridges and see what the differences between them really are.
The 6.5 Grendel vs. 6.8 SPC
Both the 6.5 Grendel and 6.8 SPC cartridges have some similarities. They function out of the same platform size as the 5.56 AR. This means that a barrel and a bolt are all you typically need to swap to make the magic happen with one of these two cartridges, though swapping a complete upper is generally a better course of action.
Both cartridges will also fit in a standard, STANAG AR15 magazine. I said they will fit, not that they will necessarily function. They might, but both cartridges have different geometry than the 5.56. This can cause them to stack differently in the magazine. It would be a good idea to purchase purpose-built magazines for the caliber you're shooting, at least until you prove standard mags reliable in your platform.
Both cartridges also fill a niche, the happy medium between the .223/5.56x45 NATO and the .308 Winchester/7.62x51 NATO. Both offer external ballistics that seem to punch above the AR's weight class with greater magazine capacity, faster follow-ups, and less recoil.
Both cartridges are 2.26" in length, the maximum allowable length for the AR platform. The 6.5 Grendel has a bullet diameter of .264 inches. The Grendel's most common bullet weight is 123-grains, with other bullets available as light as 90 and as heavy as 130 grains. The 6.8 SPC fires a .277-caliber bullet weight ranging from 75-120 grains.
Grendel ammo is loaded into a wider case with less overall case length. The base diameter of the case is 0.439" versus the 0.422" base diameter of the 6.8 SPC. This gives the 6.8 SPC slightly more overall case capacity while keeping the case a bit slimmer but at the disadvantage of requiring the use of stubbier bullets that aren't quite as effective at longer ranges.
Muzzle Velocity & Kinetic Energy
From barrels of the same length, the Grendel and SPC cartridges perform similarly. The 6.5 really shines at longer ranges, however. With a shorter case length, it utilizes longer bullets, giving it a higher ballistic coefficient. The 6.5 Grendel was designed to be fired from a minimum barrel length of 20 inches. While it can be fired from shorter tubes it tends to lose a lot of its potential.
When fired from the longer barrels it was optimized for, the 6.5 Grendel with its higher ballistic coefficient, offers a flatter trajectory than the 6.8 SPC. This difference tends to become greater as the distance increases, and the skinny 6.5 bullets are also much less susceptible to wind drift than the wider 6.8 bullets. If your intent is to shoot beyond, say, 600 yards the Grendel is probably your best bet, though these differences are pretty slight.
On the other hand, the 6.8 SPC was designed to be shot from shorter, 14.5" barrels of military M4s. From the muzzle the 6.8 SPC offers greater velocity and greater kinetic energy than the Grendel from shorter, 16" barrels. If you desire a superior performance from a shorter barrel and your ranges are inside 600 yards the 6.8 SPC is definitely a contender.
Most experienced adult shooters will find neither cartridge has punishing recoil. Both have more recoil than 5.56, yet both are extremely manageable. That said, the Grendel cartridge does have more felt recoil than the 6.8 SPC. Again, neither is painful or difficult to control, but this is another feather in the quiver of the 6.8 SPC being the preferred close quarters round.
Moderate amounts of recoil reduction can be easy to overlook by experienced shooters. A little less recoil can make a big difference to kids or the recoil sensitive. The 6.8 SPC's lower recoil might be important to a kid on his first deer hunt. In these instances, long-distance shooting is rarely the priority, but accuracy always is. A little less recoil can go a long way.
Both of these cartridges offer plenty of practical applications. Since both chamber in traditional, AR-platform rifles, they make excellent candidates for a ballistically-upgraded AR. Both the 6.5 Grendel and the 6.8 SPC offer at least 40% more power than the 5.56. As we have seen, the 6.8 delivers a slight advantage up-close and the 6.5 performs slightly better at distance.
Both offer a serious lethality upgrade. Though gaining favor, the 5.56 has been somewhat debatable as a hunting round. Heavier, larger-diameter bullets that both the 6.5 and 6.8 cartridges have are probably better suited to hunters of medium, thin-skinned game. While not quite at traditional, .30-caliber hunting load energy levels, these cartridges pack plenty of power for clean kills on mule deer, feral hogs, and similarly sized game.
Both would also be inherently practical for self-defense applications. Again, the ballistic superiority of the two over 5.56 at close range is undeniable. It is easy to imagine law enforcement applications, as well. While performing well up close and personal, both perform pretty well at distances outside of typical self-defense ranges, but at ranges well within the realm of plausibility for LEOs.
One practical consideration is ammunition availability. The 6.5 seems to be more popular, and Grendel ammo is more readily available on the market than 6.8 SPC loadings. Of course, this only applies if one is limited to factory ammo for one reason or another (LE or defensive use coming to mind). If one reloads, the sky is the limit.
The Bottom Line
There are some differences between these cartridges. An easy way to think about is the 6.8 SPC hard-hitting terminal performance at close range, while the 6.5 Grendel has longer legs and retains good energy for much longer. If you need the longer range, the 6.5 is your best bet, and if you want a cartridge that performs optimally from a shorter barrel, go with the 6.8 SPC. Really though, the differences are pretty small for about 99% of hunters and shooters out there, so you probably won't go wrong with either.
The SOTA Arms Difference
The AR15 is a tremendously versatile rifle. Part of that versatility is the ability to utilize the right cartridge for the job. The 5.56 isn't the answer for everything. If you need to get more power out of your existing platform, you may consider moving up in caliber to a 6.5 Grendel or 6.8 SPC. SOTA Arms offers everything you need to step up to a bigger-bore AR. As a side note, the feedback Sota Arms gets from it’s customers is the 6.8 shoots very well out to 600 yards and and with the 6.8 Grendel, out to 1,000 yards.
The differences between both of these cartridges are pretty small. For what 99% of hunters need either will answer the mail. Regardless of which caliber you choose, SOTA Arms offers complete uppers in both 6.5 Grendel and 6.8 SPC. Both of these are in the "correct" barrel length, with most Grendel offerings with a longer barrel of 20 inches. The 6.8 offerings all come with the 16-inch barrel from which the 6.8 performs best. A wide variety of options are available including black or naked stainless barrels and Key-Mod and M-LOK handguards.
If a complete upper isn't your thing and you want to completely re-chamber your rifle, SOTA has got your back. Both the 6.5 and 6.8 only require a barrel, bolt carrier group, and magazines to change calibers, and we carry top-of-the-line versions of all three. If you decide neither the 6.5 Grendel nor 6.8 SPC meets your needs, SOTA Arms carries uppers and upper parts in a variety of other chamberings, as well.
Back the Blue
To show support to our police officers that put their lives on the line every day, we offer a customized AR15 rifle that has been royal blue cerakoted with the battleworn finish. The ejection port cover door has also been customized. This is offered in various calibers.
Guns of Color
Featuring a collection of AR-15 Rifles. Sota Arms guns of color are customized with various techniques using Cerakote or Anodize. No two guns are alike. Spice up your collection with a gun of color. You’ll be the envy of all your friends.
Complete Upper Units
Sota Arms complete upper units are COMPLETE with bolt carrier group and charge handle. Don’t be fooled by others that claim the upper is complete when it doesn’t have the charge handle nor the bolt carrier group. We have plenty of options from various barrel lengths, handguard lengths and calibers, to name a few.
Sota Arms always test fires every complete upper as it’s final quality check to verify cycling.
If you are looking for a complete upper unit, SOTA Arms has you covered. We carry AR 15 uppers in a variety of calibers like 6.5 Grendel, 5.56, .300 Blackout, .224 Valkyrie, and more! We also offer .308 complete AR 10 uppers. Don't be fooled. Other companies may offer "complete upper receivers" that don't actually come with the charging handle and bolt carrier group. Our complete upper units come with the upper receiver, M-Lok or Keymod handguard, charging handle, bolt carrier group, gas block, muzzle device, and rifle barrel. Each caliber has tons of options to choose from with varying barrel lengths, twist rates, hand guard lengths, and gas block styles.
Our complete upper units are crafted using 416R stainless steel or 4150 Chromoly barrels and given a black R3 Anodized finish on the upper receiver. These uppers are designed to drop onto a Mil-Spec lower receiver. We manufacture all of our AR-10 and AR-15 parts and components in-house, right here in the USA. Your next AR-15 or AR-10 build starts here. Trust us to set you up for success and buy American with PRIDE!
AR-15 Complete Lowers & Assemblies - All U.S.A. Manufactured by Sota Arms.
Start your AR-15 build with a stripped or fully assembled AR-15 lower receiver from Sota Arms. Our lower receivers are manufactured on State of the Art CNC Machines, made with BILLET aluminum, not forgings, and come in a variety of configurations to fit you perfectly. We offer FFL’s variance lowers, which equates to us engraving your company information and each lower. From complete kits to individual pieces, Sota Arms has the lower parts you need to build your ultimate AR-15.
Shop accurate and affordable AR-15 barrels manufactured and sold by Sota Arms.
Our AR15 barrels are available in various lengths, and finishes. We offer a wide variety of profiles for your individual needs including M4, H-bar, and SOCOM profiles. Our barrels are made with the finest 4150 Chrome Moly Vanadium or 416R Stainless Steel and button rifled for maximum accuracy! Our customers’ feedback is they get 1.0 MOA with no problem.
When your done shooting, please remember to always keep your barrel clean and aggressively chamber brush the barrel.