A Complete Guide to Alternative AR-15 Rounds

When it comes to the AR-15, you have a broad selection of rifle calibers, and many of those are widely available at local gun stores, online dealers, and at everyone’s favorite gun shows. Most shooters will choose the well-known .223 Remington or 5.56x45mm rounds. Both are common, cost-effective, and offer adequate stopping power.

But occasionally, when you are tired of shooting the same old round, you want to mix your shooting experience up with, say, 6.5 Grendel or .300 Blackout.

How to Select an Alternative AR-15 Caliber

Picking out a new round for an AR-15 project is not always straightforward. For most, you will require a new upper for your rifle. It can be quite costly.

So, with that in mind, choosing a caliber comes down to a few key factors, such as:

• Power — Depending on your intended use for your AR-15, stopping power may come into play. You want a round capable of dropping your hunting prey or plinking a target with relative ease.
• Availability — It would not do to invest in an upper for 6.5 Grendel, only to discover that most stores in your area are routinely sold out of the round.
• Cost — In the case of ammunition, cheap does not equate to a bad round. In fact, the most affordable rounds on the market are usually the most widely used, making them some of the best available.

Alternative Ammunition at a Glance

Instead of using the standard 5.56 round, you have a few options for an AR-15, including:

• .300 Blackout — Relatively expensive, though the cheapest of the alternative AR-15 calibers, the .300 Blackout requires a barrel change and is an ideal round for home defense, hunting, and range shooting.
• 6.5 Grendel — More expensive than the .300 BLK round, 6.5 Grendel requires a new barrel, bolt, and magazines to operate. Most use the 6.5 round for competitive shooting and hunting large game.
• .458 SOCOM — Far more expensive and requiring a new barrel and bolt, the .458 SOCOM round is typically used for hunting with the AR-15 platform.
• .50 Beowulf — The most expensive alternative AR-15 caliber imaginable, .50 Beowulf excels at taking down big game while hunting, though you will require a new barrel and bolt.

.300 Blackout

The .300 BLK is arguably one of the most popular alternative AR-15 calibers on the market. The round features a .223 case, with a heftier .30 caliber projectile.

Most use the .300 Blackout round for hunting deer and the occasional wild hog. For anything at ranges of 250 yards, the .300 Blackout drops significantly and fails in comparison to other rounds.

6.5 Grendel

The 6.5 Grendel round is built around the 7.62x39 case, which is the same case used for the iconic AK-47 and utilizes a .264 caliber bullet. Unlike .300 BLK, the 6.5 Grendel round is well-known for providing exceptional ballistic performance at ranges. When fired, the Grendel round is rarely affected by crosswinds, and as such, is often used for hunting deer up to 300 yards away.

.458 SOCOM

The .458 SOCOM round was initially designed for close-quarters battle (CQB) purposes. The cartridge is a slimmed version of the .50 AE designed specifically for .458 caliber projectiles. Overall, it is a heavier bullet built to produce massive kinetic energy when fired.

Ideally, you will use a subsonic round and a suppressor with the .458 SOCOM. It functions well with both/either one.

.50 Beowulf

If you look back to our “at a glance” section, you will note the .50 Beowulf is the most expensive alternative round available for the AR-15. It is also the strongest. If you use .50 Beowulf for hunting purposes, it will tackle any big game you come across.

The downside is, of course, the cost and the immense recoil produced by the round. After all, this is a bullet designed to stop vehicles.

While 5.56 is the most common round to fire from an AR-15, you can build a rifle capable of firing any of the alternative rounds we mentioned here. If you want to start now, we have 80% lower receivers available to kickstart your next build!