5.7x28 vs 5.56

So, you’ve been searching for a new 22 caliber centerfire and stumbled upon the 5.7x28 and the 5.56x45. Although they may be shaped similarly, the 5.7 and 5.56 are very different cartridges with very different capabilities. In this article, we will be going over these differences to help make your decision a little easier.

Physical Attributes

Stood side by side, you’re probably thinking there aren’t any similarities shared between the 5.7x28 and the 5.56. Although dimensionally they are very different cartridges, both the 5.56 and the 5.7 utilize the same .224 diameter bullets. While this does mean they can be loaded with the same bullets, they almost never are. In fact, the 5.7 is typically only loaded with bullets weighing up to 40 grains, whereas the 5.56 extends this range up to 77 grains. It should be noted that both cartridges can be loaded with heavier bullets than mentioned, though they are typically subsonic offerings (when fit in traditional length magazines).

Looking past bullet diameter, however, you will notice just how different the cartridges are dimensionally. In fact, the 5.56 dwarfs the 5.7 in every other measurement. Starting with the length, an empty 5.7x28 case has a nominal length of 1.138 inches. By comparison, the 5.56 has a nominal case length of 1.760 inches. On top of being nearly 5/8ths of an inch longer, a 5.56 case is also wider than a 5.7 case. This width starts at the base of each case, where we find that the 5.56 has a 0.378-inch rim diameter compared to the 0.307-inch rim diameter of the 5.7. As you can imagine, this extra length and width gives the 5.56 a distinct advantage when it comes to case capacity. This not only equates to more volume for powder, but it also allows the 5.56 to use much heavier bullets more effectively as mentioned previously.

Power

When it comes to power, there is a substantial difference between the 5.56 and the 5.7. Although you probably already guessed that the 5.7 loses this segment, the factory specifications may be a bit misleading. When looking at the Hornady 5.56 62-grain FMJ, we see that it produces 1,289 ft/lbs. at a muzzle velocity of 3,060 feet per second. By comparison, the Hornady 5.7 40-grain V-max produces 291 ft/lbs. at a muzzle velocity of 1,810 feet per second.

While there is a significant difference in these figures, with the 5.56 producing nearly 4.5 times more energy than the 5.7, they are a bit misleading. Being that the 5.56 is primarily chambered in rifles, the figures mentioned were referenced from a 24-inch barrel. The 5.7 on the other hand, is primarily chambered in handguns, so its figures were taken using a 4.8-inch barrel. Although it is true that the 5.7 will never match the performance of the 5.56, it does come much closer than the factory values would have you believe when both cartridges are fired from the same barrel length.

It should also be noted that the 5.7 is much more efficient than the 5.56 when both are fired out of pistol length barrels. This efficiency is primarily because the 5.7 is most often loaded with fast burning pistol powders, whereas the 5.56 is primarily loaded with much slower burning rifle powders. Faster burning powders help bring the 5.7 up to speed more quickly than the 5.56, though it still will not be as powerful, even out of pistol length barrels. It should also be noted that when it comes to rifle length barrels, especially past 16 inches, the 5.56 gains significantly more velocity than the 5.7, due to its slower burning powders.

Price

Requiring significantly more materials to produce, you would think the 5.56 is more expensive to shoot than the 5.7, right? While it does require more materials, the 5.56 is often cheaper to shoot than the similar load offerings in 5.7 (at least currently).

There are several factors that lead to these lower/similar costs, but perhaps the biggest reason, is the massive popularity of the 5.56. In fact, the 5.56 is currently one of the most popular centerfire rifle cartridges on the market. Not only is it popular on the civilian market, but also when it comes to the military as well. Massive popularity not only leads to more ammunition choices, but it also leads to much larger production runs than the 5.7. These large production runs greatly decrease the costs involved with loading a single cartridge, which ultimately lead to the lower/similar prices. It should be noted, however, that more companies are beginning to produce load offerings for the 5.7 due to its increasing popularity. Although this should only drive prices down in the future, realize they likely won’t drop below 5.56 any time soon (if at all).

Benefits of 5.7x28

With all its shortcomings, you may be wondering why anyone would possibly choose the 5.7x28 over the 5.56. While it’s small size cannot compete with the performance of the 5.56, the 5.7 does offer some unique benefits over the 5.56. Due to its size and pressure, the 5.56 cannot fit in a conventional semi-automatic handgun design, whereas the 5.7 could not be more at home. With its somewhat narrow case dimensions, the 5.7 can also fit more rounds in the same profile as conventional handgun bullets such as 9mm.

On top of its ability to fit in smaller places, the 5.7 weighs less than the 5.56 while taking up less room. This means if kept within the same weight parameters, you will be able to carry significantly more ammo than the 5.56, which could be a huge benefit to some.

5.7 or 5.56?

While the 5.56 and the 5.7 are firing the same diameter projectiles, they are very different cartridges in nearly every other respect. With these major differences, the main question you’re probably wondering is which one should you get?

Although the 5.7 does not offer a lot of benefits over the 5.56, its size may be what you’re after. While the 5.56 requires a substantial platform to function safely, the 5.7 is small enough to fit in conventional sized handguns. With blistering velocities out of short barrels, the 5.7 makes for an excellent cartridge for those looking to be as compact as possible.  

If you’re looking to save money at the range however, you will not be doing so with the 5.7 when compared to the 5.56. In fact, the 5.56 is one of the most popular cartridges in existence, which equates to cheaper ammo costs on average. On top of its popularity, the 5.56 beats the 5.7 in every performance metric, which lends well to longer range shots and more retained energy.

Perhaps the most important question to answer, is whether you’re after size or performance? Regardless of which direction you go, realize that you are getting a great cartridge either way.

--Banana Ballistics