AR-15 Magazine Guide — Part 1

The most finely made semi-auto firearm in the world isn’t worth a damn without two crucial components: quality ammunition and magazines. Without these two parts of the equation, any magazine-fed firearm quickly becomes a frustratingly unwieldy, single-shot nightmare.

Thankfully, during the last few decades, magazine development and design have kept pace with the prolific AR15. So America’s favorite black rifle now has a dizzying array of magazines available for it. These range from single-shot to ultra-capacious drum magazines and are constructed from steel, aluminum, and even high-impact polymer.

With so many AR-15 magazine options available, picking the best one for a shooter can seem like a truly daunting affair.

In response, the editorial staff here at, are assembling a few handy guides to make the buying process easier.

Now, since the AR15 market is so vast, it’s important to first determine a shooter’s needs and desires before deciding on anything. A bench rest shooter who needs to keep his rifle as low as possible doesn’t want or need a Magpul D60 drum, just as a three-gunner would not appreciate a flush-fitting five-round magazine. Both magazines are tremendously effective in their given roles, but ill-suited to others.

The first installment of this guide will focus on narrowing down one major aspect of a magazine design—capacity.

Though I already have to stop and add one caveat.

Certain states and even counties within the United States fall under magazine capacity legislation. These stem from a now-expired national law colloquially referred to as, ‘The A… Weapons Ban’ or AWB. In the AWB, magazines capable of holding more than ten cartridges were limited to law enforcement and military use only. Shooters buying used magazines previously owned by police who bought them during the ban will often see ‘LEO’ written on them with a date. LEO is an acronym for Law Enforcement Only. – If you’re living in a state without a ban, this stamp is meaningless.

What about shooters living under such restrictions?

They should take a look at our simple guide to magazine capacity laws.

Everyone else should continue reading.

So you’re all set with legal restrictions, and want to narrow down your search for your first bullet-feeding device.

The first step is to determine your rifle’s focus.

If you own a varminting bench rest rifle tipping the scales at 15 pounds, you’re going to want something fairly streamlined and low profile. Assuming no hunting capacity restrictions, the longest magazines that don’t protrude past the pistol grip of an AR-15 is the 20-round straight magazine.

Note: Some manufacturers build limited capacity mags from full-capacity bodies. These are great for capturing the aesthetics of standard-capacity 30-round mags, but negate the low profile of magazines designed for 20 rounds of ammunition.

Vietnam-Era 20 round AR-15 magazine
Vietnam-era AR-15 magazines

These types of magazines will be immediately familiar to anyone who has seen footage of the Vietnam War. US Soldiers in Vietnam armed with the original M16 were issued a few aluminum 20-round magazines. The short length of these magazines allowed infantryman to fire their rifle while prone, or laying down. While these magazines often get a bad rap for being unreliable, they’re actually quite good if properly maintained. Though the biggest issue with them, like all aluminum magazines, is durability—step on an empty aluminum magazine once, and odds are it won’t feed correctly ever again.

What about classic 30-round AR-15 magazines?

These are the jack-of-all-trades of the AR-15 magazine world. Not quite perfect for anything, but more than good enough for everything. The best part about 30-round magazines is compatibility and commonality.

Nearly every AR-15 magazine carrier on the market today is designed for a standard 30-round magazine. These are the most ubiquitous and affordable magazines available for the AR-15 platform. Dozens of manufacturers make them in dozens of colors, but they all adhere to STANAG guidelines.

STANAG 30-round AR-15 Magazine.
STANAG 30-round AR-15 Magazine.

STANAG, or Standard Agreement NATO, is a set of design guidelines that list every conceivable aspect of the 30-round AR15/M16 magazine’s design. The purpose of the agreement is to ensure magazine compatibility between member armies of NATO in times of crisis.

But I digress, these magazines are great for three-gunners as they strike a great balance among weight, capacity, and size. They’re not so large as to snag on obstacles when running, but still offer shooters a respectable amount of in-rifle ammunition supply that doesn’t ruin the gun’s balance or user’s back.

Higher-Capacity, Non-Drum Ar-15 Magazines

Magpul 40 round polymer magazine beside STANAG mag.
Magpul 40 round polymer AR-15 magazine beside STANAG mag.

Other common magazines in competitive circles are 40-round or greater variants. Some of these are simply a standard 30-round magazine body with a replacement baseplate that facilitates more ammunition, while others are purpose-built.

Most shooters shy away from these as they seem awkward, but they’re great for extended plinking at the range and especially run-and-gun competitions where shooters aren’t penalized for magazine capacity. Certain shooting sport disciplines like three-gun or steel challenge feature stages with target-rich environments.

Shooters racing the clock to engage these targets will often go too fast and miss several, costing them precious seconds. Miss enough, and you’ll be forced to perform a magazine change in the middle of the stage, and waste even more time. For these instances, less isn’t more. More is more, so competitors want as much ammo as they can carry. So when 40 or 45-round mags aren’t enough, they turn to drums.

Drum Magazines

Drum magazines are named for their resemblance to the percussion instrument with the same moniker. These ultra-capacious magazines use a giant clock spring to wind ammunition around an outward spiraling cylinder.

These mags hold anywhere from 50 to 120 rounds of ammunition and can feature either a single, or pair of drums like the Beta Company drums. Drums are great for three things. Plinking, certain competitions, and photographs; nothing makes a gun look meaner than a giant drum hanging off it.

KCI clear 100-round AR-15 drum magazine.
KCI clear 100-round AR-15 drum magazine.

Almost like an instrument of freedom.

Whichever capacity a shooter determines is best for them, it’s important to practice with it regularly. Rapidly slamming home a 30-round Magpul PMAG is worlds apart from trying to quickly change BETA C drums. Stay tuned for our AR-15 Magazine Guide — Part Two, coming next month as part of our giant magazine-buying guide for the AR-15.

Jim is a freelance writer for dozens of firearm publications, the host of the YouTube channel Burst Review and the youngest author to write a cover story for Shotgun News in its 86-years of operation. Jim loves anything that goes, ‘boom’ but particularly enjoys military firearms from the Cold War and WW2. When he’s not slinging lead downrange he can be round hiking in the mountains with his wife Kim and their vicious attack dog, Peanut.

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