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Unlike a specific gun, AR 15 is a platform. This implies that one can use various parts and make it shoot several calibers. Though the original AR 15 caliber is 5.56 or .223, the platform is currently chambered in several other calibers. In fact, some calibers are designed explicitly for AR 15 rifles.
In simple terms, AR 15 caliber can literally be anything you think it can be. The most popular chambering include.300 Blackout, 9mm and.22LR. With a fat wallet, some custom AR builders will deliver a gun in any configuration of your preference.
The Originals: The 5.56 and .223
As mentioned earlier, any AR 15 caliber arose from the immemorial 5.56 and the .223. The 5.56 is light and bullets are in the typical range of XX grains. Additionally, the rounds leave the barrel at high velocities of approximately 3,000fps (feet per second).
A typical AR 15 mag carries a whopping 30 rounds, and they are reasonably light. One can actually take with him a few hundreds of 5.56 rounds with a lot of ease. This makes it favorable for soldiers.
On the other hand, the .223 rounds are meant for civilian sales and thus regulated by the SAAMI.
Although it is mostly used interchangeably with 5.56, the features of the two are not similar, as most people argue. Despite their closeness, 5.56 is somewhat a more powered .223. However, their outsides are just but identical.
In this case, one can use a 5.56 round in a .223 chambered rifle, but the reverse is not advisable. There is a fear that .223 might not effectively handle increased pressure from the 5.56 since it’s slightly more powerful. The additional stress can cause some problems, although not a critical failure.
Most people prefer the .223 since there are various rounds readily available, with some at decently low prices.
Most Common AR 15 Calibers Alternatives
It is also popularly referred to as 300 BLK or as 7.62×35mm. Designed as an intermediate cartridge, .300 AAC Blackout is still compatible with the existing 5.56 chambered AR 15 type rifles.
From the beginning, .300 AAC Blackout was developed to offer similar ballistics to that of the 7.62x39mm. For instance, it is used in the AK-47 rifle series while yet using standard AR-15 magazines.
The .300 AAC has an effective range of approximately 460 meters. It is also characterized by a relatively lower velocity and shorter bullet drop. However, when compared to the 7.62x39m, .300AAC rounds provide better ballistic coefficients. When contrasting the coefficients for both, there is an assumption that round shots are from barrels of similar lengths.
More than often, people wonder why it is not wise to chamber an AR-15 for the 7.62x39mm. This is because 7.62x39mm rounds come with cartridge tapers, which makes them inefficient for AR 15 magazines. Otherwise, it would result in reliability problems.
.300 Blackout Pros and Cons
This caliber offers a wide variety of various bullet types. It is also ideal since it provides ballistics that are even better than that of the 7.62x39mm. Besides, it allows insignificant velocity loss when fired from shorter barrels.
On the contrary, factory ammunition is costly and hard to find. Also, similar to the 7.62x39mm, .300 Blackout is less proficient for long-range shooting. The 460 meters mentioned earlier are on the higher end, and hence sticking to less than 300 meters is better.
It is also commonly referred to as 6.5x39mm. Just like .300 AAC, 6.5mm Grendel is an intermediate rifle cartridge configured for the AR 15. While the .300 Blackout was developed to complement the 7.62x39mm, 6.5mm Grendel was primarily designed as a low recoil and high accuracy ammunition for medium to long ranges – up to 800 yards.
Since its development, the 6.5 Grendel has been a very versatile caliber. As a result, it is currently being embraced for other rifle platforms after the AR 15. This includes different types of bolt action rifles and the AK-type rifles.
In the ballistic regard, the 6.5 Grendel is significantly better than the 5.56x45mm NATO.
The 6.5 Grendel Pros and Cons
The 6.5 Grendel upper is entirely and perfectly compatible with a 5.56 lower. Therefore, if planning to improve your AR 15’s ballistics, replace the 5.56 lower with the 6.5 Grendel upper. It also enhances perform