Top 5 Calibers For The AR-15

AR-15 caliber options overview

The hosts introduce the AR-15 as a highly modular platform with far more options than just 5.56 NATO. They note that builders can configure rifles from .22 Long Rifle up to large cartridges like .50 BMG and .50 Beowulf. The discussion focuses on choosing calibers based on availability, cost, and function, including roles such as long range, close-quarters use inside a house, and hunting various game. They set up a countdown of their top five AR-15 calibers to build or buy, emphasizing how different cartridges can better match specific purposes while still taking advantage of the familiar AR-15 ergonomics and parts compatibility.

9mm AR builds, mags, and suppression

For the number five spot, the hosts select 9mm in the AR-15 platform. They show a registered SBR lower with a CMMG Banshee upper using a radial delayed blowback system, fed by Endomags that fit a standard AR-15 magazine footprint but are dedicated to 9mm. Other examples include a Banshee using Glock magazines and a Springfield Saint pattern carbine using Colt-style stick magazines. They highlight how 9mm ARs can be built as very short, compact packages suitable for close-quarters roles and are well suited to suppression. Using 9mm allows training with familiar controls, reusing existing AR magazine pouches, and potentially gaining a bit of extra velocity from longer barrels while keeping recoil and cost manageable.

6.5 Grendel and 6mm ARC long-range roles

In the number four position, the hosts discuss 6.5 Grendel and 6mm ARC as related options for extending the AR-15’s effective range. They explain that 6.5 Grendel is based on the 220 Russian case, sharing some traits with 7.62x39 but requiring different bolt geometry for reliable feeding. 6.5 Grendel is described as an intermediate step between 5.56 and 7.62 ARs in cartridge weight and recoil, while delivering more energy at distance. They then compare it to 6mm ARC, which uses the same parent case but improves long-range performance with less bullet drop, higher retained velocity, and more energy at 1,000 yards. Both cartridges can generally use the same magazines, though dedicated 6mm ARC mags exist and can be expensive. The hosts note that 6mm ARC performs well even in shorter barrels, making it attractive for compact “mini recce” or scout-style rifles aimed at medium to longer-range shooting.

450 Bushmaster and 458 SOCOM big-bore choices

For the number three slot, the conversation turns to big-bore AR-15 options, splitting focus between 450 Bushmaster and 458 SOCOM. 450 Bushmaster is highlighted as a straight-walled cartridge, which makes it suitable for hunting in states that require straight-walled rounds and restrict necked cartridges. Its .45-caliber projectiles and heavy bullets deliver substantial energy for larger game such as elk. In contrast, 458 SOCOM is a necked cartridge originally developed for specific military roles and later adopted for hunting and other uses where a large-diameter bullet is desired. The hosts show a 458 SOCOM magazine that uses a standard STANAG-style body but with a different follower and spring, effectively making it a single-stack design that holds about 10 rounds. They note that both 450 Bushmaster and 458 SOCOM can work with AR-15 pattern magazines, though capacity is reduced due to the larger cartridge dimensions.

Why 300 Blackout excels in short barrels

At number two, the hosts feature 300 Blackout as a particularly versatile AR-15 caliber. They emphasize that it performs best in short-barreled configurations, especially under roughly 9 inches of barrel length. The cartridge supports both supersonic and subsonic loads, allowing builders to tailor setups for compact, suppressed use or for more energetic supersonic performance. An example shown is an 8-inch 300 Blackout build paired with a suppressor, resulting in a very quiet and compact rifle that still delivers substantial impact at closer ranges. The hosts argue that 300 Blackout is not just a niche option, but a flexible choice for close-quarters roles, suppressed shooting, and hunting within its effective distance, all while staying within the familiar AR-15 platform.