When comparing cartridges like 6.5 Grendel vs. 5.56 NATO, getting in deeper into a substance is always recommended to get a better image of both calibers.
The US Army was the first in the world in 1937 to introduce a semi-automatic rifle into its arsenal as a standard-issue service rifle – the .30-06 Garand M1. But during the last days of the Second World War, the US military analysts concluded that there was a need for greater infantry firepower, that is, the need for selective fire weapon, the forerunner of today’s assault rifle.
The concept was based on German experiences with the shortened cartridge 7.92×33 mm for the famous StG 44 “machine carbine.” Following that concept, the US military developed a .308 T65 (7,62×51 mm, a future 7,62 NATO) and, in 1959, adopted the M14. The new battle rifle gradually replaced the M1 Garand in the US Army and other branches and became the primary infantry rifle in Vietnam.
|Bullet||90 to 130 gr (6.0 to 8.0 g)||50 to 77 gr (3.56 to 5.0 g)|
|Bullet diameter||0.264” (6.7mm)||0.224 (5.7mm)|
|Case length||1.52” (38.6mm)||1.76” (44.7mm)|
|Maximum overall length||2.26” (57.4mm)||2.26” (57.4mm)|
|Rim diameter||0.44” (11.1mm)||0.378” (9.6mm)|
|Max Pressure (SAAMI)||52,000 psi||55,000 psi|
|Muzzle Velocity||120 gr/ 2,610 fps||55 gr/ 3,165 fps|
|Muzzle Energy||120 gr/ 1,815 ft-lbs.||55 gr/ 1,223 ft-lbs.|
|400yds Bullet Drop & Energy||-32.1” 902 ft-lbs.||-23.1” 385 ft-lbs.|
|Powder load||26 gr||24 gr|
|Rifle Weight||6.0 lbs.||6.0 lbs.|
|Free recoil energy||9.12 ft-lbs.||4.45 ft-lbs.|
|Case capacity||35.0 gr H2O||31.4 gr H2O|
History Of The 5.56 NATO
However, the relatively new M-14 rifle and 7.62x51mm cartridge were soon replaced with a futuristic, more ergonomic rifle and smaller and lighter .22 caliber round. The high-velocity 5.56x45mm cartridge was spawned from the .222 Remington, the first rimless cartridge for civilian use in the United States.
The idea of using smaller cartridges was based on the fact that infantrymen could carry more ammunition without weighing them down. Translate to numbers; a soldier can carry roughly three times as much 5.56mm as 7.62mm and fire it from the lighter assault rifle with more controllable firepower.
It’s a well-known story that the new M-16 rifle and 5.56 cartridge saw some growing pains in its early days. After initial problems with the rifle and ammunition, the development team solved most of the reliability problems that plagued that rifle-cartridge system.
The new 5.56, usually pronounced “five-five-six,” weighs less than half than 7.62mm and has four times less free recoil energy than the 7.62 x51 NATO. Compared to a 20-round magazine loaded with full-power 7.62 cartridges, the fully loaded 30-round AR-15 magazine is lighter by almost two ounces.
When adopted by the US military, the initial 5.56x45mm M193 cartridge was loaded with traditional 55-grain full metal jacket bullets. The conventional FMJ bullet was sited in 1.760 in (44.70 mm) case allowing for a maximum overall length of 2.260 inches or 57.40 mm in the metric system.
The original .224″ caliber projectile was fired at 3,250 feet per second and generated 1,290 foot-pounds of energy. This tumbling 55-grainer is a truly violent bullet that makes a broad but shallow wound channel at ranges inside 100 yards.
At this point, we will only refer briefly to the fact that 5.56 soon after being introduced to the military, got the twin brother designed for the civilian market. Though the .223 Remington is highly similar to the 5.56x45mm, technically, its dimensions and chamber pressures are not identical. Due to the much higher pressure that can damage the shooter or rifle, the 5.56x45mm rounds should NOT be loaded into .223 commercial chambers.
The civilian version of the 5.56 NATO cartridge, the .223 Remington, was released in the early 1960s, and since then, this centerfire .22 caliber round has recorded tremendous commercial success throughout the whole planet.
Although 5.56 has a flat trajectory, it’s not best suited for hunting out past 400 yards as its velocity starts to drop off by the time it reaches that distance, and muzzle energy usually drops below 500 ft-lbs.
Without a doubt, the 5.56x45mm is modern combat ammunition designed for the modern battlefield. Compared to classic battle rifles chambered for high-powered cartridges, the tiny 5.56mm packs a substantial increase in ammo capacity with a considerable decrease in weight.
However, the lighter 5.56 ammunition is also lighter in ballistic performance. Although the US Army Technical Manual claims that the 5.56 NATO cartridge has a 547-yard range for a man-size target, civilian needs are quite another thing. The minimum impact energy required for humane or ethical hunting whitetail is 1,000 ft-lbs. When you look at ballistic tables, you’ll see the 5.56 might not deliver the required power at a range of more than 100 yards.
The general consensus holds that the 5.56 works well for predator/varmint hunting and target shooting, but it performs poorly on bigger game or at larger distances. That was a starting point for many designers to set about developing larger bore alternatives that would be more powerful than the 5.56mm NATO but would still function in M4/AR-15 rifles.
Like many other AR-15 compatible cartridges, the 6.5 Grendel was developed as an alternative to the 5.56x45mm NATO in 2001.
Rather than some big bore options, the intermediate 6.5 Grendel can be fired from the AR-15/M16/M4 weapons without extensive internal modifications. Actually, the 6.5 cartridges will require only changing the barrel and bolt since it can use regular M16 rifle/M4 carbine magazines. Of course, the capacity is slightly decreased as a standard STANAG 30-round magazine will hold 26 of 6.5 Grendel rounds.
In comparison to the original M16/AR-15 caliber, the 6.5 Grendel was designed to allow using AR-15 rifles at extended ranges from 200 to 800-yards.
The mastermind of this project was a British-American armorer Bill Alexander of Alexander Arms, and notably, Finish ballistician Janne Pohjoispää from Lapua. Applying huge experience based on his previously released .50 Beowulf round, Bill Alexander designed, this time, a medium bore option that could reach out a bit farther than genuine caliber.
While the other medium bore rounds like the .300 AAC Blackout or 6.8 Remington SPC provide extended firing capabilities of the black rifle up to 300- or 400-yard at best, a 6.5 Grendel not only packs more power than a 5.56x45mm NATO but its effective at 500-plus-yard ranges.
The 6.5 Grendel doesn’t only deliver impressive downrange energies, but it is capable of tack-driving accuracy in the right hands. The secret of this hard-hitting long-range cartridge is associated with intermediate 6.5mm cartridges and a broad spectrum of bullet weights.
But let’s see the roots of this popular cartridge. While many consider the 6.5 Grendel (6.5x39mm in metric system) as the western counterpart to the 7.62×39 Kalashnikov round, one could rather say the 6.5 Grendel is a successful combination of time-tested military cartridges and modern competition shooting calibers.
As an alternative intermediate AR cartridge, the 6.5 Grendel is based on the benchrest-proven 6.5 PPC, which in turn used a .220 Russian (far cousin of the 7.62 x 39mm) cartridge as a parent case.
Compared to 5.56, the 6.5mm Grendel has a shorter case (1.76” vs. 1.52”) but a slightly larger case capacity. On the other hand, the 6.5 cartridge uses a larger diameter bullet than 5.56x45mm (.264″ vs. 224″).
The 6.5 Grendel is a flexible round as it is available with bullets ranging from 90 to 140 grains compared to the 35-77 grain range of the 5.56 factory loads. The most common 6.5 loads come with 90, 100, 120, and 129 grains offering 22-73% more energy at the muzzle than 5.56.
With a 1.52” (38.6mm) short case, the 6.5 Grendel can accommodate long-ogive 120-grain and 130-grain bullets and keep a 2.255″ overall length to sit cartridges into AR-15 magazines. However, in a bolt-action rifle, you can load even heavier and longer projectiles up to 140 grains with an overall length of up to 2.420″, making it an ideal combo for more extended range or tactical shooting applications.
The 6.5mm bore diameter provides about 39% more frontal surface area than the tiny 224” bullets, resulting in more kinetic energy at all ranges and better penetration. Regardless of Grendel’s long-range capability and significantly more power than the 5.56 cartridge
Although Grendel has approximately twice as much free recoil as the 5.56, it is a pretty manageable recoil.
Delivering larger kinetic energy at a longer effective range with less wind drift, the 6.5 Grendel is definitely ballistically superior to the 5.56. As a negative, 6.5 Grendel can have a significantly shorter barrel life, degrading the accuracy noticeably after 4,000 to 5,000 rounds fired.
Undoubtedly, the 6.5 Grendel provides a level of ballistic performance unavailable in the original AR-15 platform. Even though the 6.5 Grendel is significantly more powerful than the 5.56×45, it is still a moderately powerful, all-around cartridge effective on a deer-sized game.
The 5.56 NATO is an outstanding varmint hunting cartridge with significantly less recoil than the 6.5 Grendel and considerably cheaper ammunition.
With more than 50 years experience in the field and the testing lab, author L.P. Brezny is one of today’s most recognized shotgun experts and authors. He is a contributor to dozens of firearms publications, such as Wildfowl, Shotgun Sports, and Varmint Hunters, and he is a regular columnist in the Gun Digest annual as well as AmmoLand News.