Originally posted on American Partisan, revised December 2022.
There’s a reason every 4-man fire team in the US military has an automatic rifle; it’s a potent force multiplier. And while we as civilians don’t have common access to full-auto weaponry, it is possible to use a semi-auto weapon to fill the role of a full-auto one. Today I will cover why automatic rifles are useful and what you should look for when choosing/building a semi-auto version of one.
I would like to first point out that I’m not the first one to introduce the topic of automatic rifles, or at least the nearest semi-auto equivalent. Hawkeye made a pretty good article in 2018 about what he called the Area Denial Weapon, which is essentially the same concept.
Automatic rifles and machine guns are designed to lay down heavy volumes of fire to suppress or inflict heavy casualties on enemy troops. There’s a lot of misconceptions about “suppressing fire” floating around, so I’ll start by describing how suppression and fire superiority work.
The first thing that you do in a gunfight is attempt to establish fire superiority and suppress your opponent. An enemy is “suppressed” when he is too scared by your gunfire to stick up his head and place well-aimed fire on you. Once that is accomplished, you can maneuver freely and impose your will on him. On the other hand, if YOU are suppressed, the enemy can maneuver on you and your team. Fire superiority, once lost, is difficult to regain, so it is the responsibility of the team/squad leader to control rates of fire to maintain fire superiority throughout the engagement.
Suppression relies on two things: accuracy and volume. Accuracy is the most important because inaccurate fire does not suppress well. You are much more likely to duck back behind your cover if bullets are kicking up dust in front of you, chipping away at the rock you’re hiding behind, or hitting your buddies, than if they’re harmlessly snapping by 20 feet overhead. However, inexperienced/poorly trained troops can be suppressed easier than veteran troops who know the difference between effective and ineffective incoming fire, so bear that in mind when considering your opponent.
Volume is secondary in importance, but it is important. If both parties in a gunfight are equally trained, whoever lays down the heaviest volume of accurate fire establishes fire superiority. This is where an automatic rifle comes in handy. Firing in short, controlled bursts, the automatic rifleman can combine with the well-aimed single shots of the riflemen to rapidly suppress the enemy.
The advantage of automatic rifles as opposed to machine guns is that they are more accurate with their bursts, and thus accomplish the same level of suppression with fewer rounds. This makes the autorifle an ideal choice for light infantry squads who cannot always count on immediate resupply.
Building the Automatic Rifle
There are a few things you should look for in a purpose-built rapid-firing weapon to fill the role of an automatic rifle. Ideally you would buy a semi-auto version of a military autorifle, but this can get very expensive. You may choose to build your own, especially if your team is standardized around the 5.56 cartridge.
First, the weapon should be piston-operated. Direct impingement gas systems (i.e. the vast majority of AR-15s) aren’t designed to handle a large volume of rapid fire. In fact, the gas tube is designed to be the failing point on an AR if it overheats, to prevent catastrophic damage elsewhere on the rifle (meaning that when it fails, your AR is still operable, just as a straight-pull bolt action). This is why every machine gun and automatic rifle in service with the US military is piston-operated (except Ma Deuce, she’s a special beast).
Second, the weapon should have a heavier barrel to slow the speed at which it heats up. If your barrel overheats, it can warp, killing your accuracy (and you if you’re not careful). I’m not saying that heavy barrels don’t overheat, just that they don’t overheat as quickly. Heavy barrels are fairly easy to get for AR-15s, commonly sold as “match-grade” or “competition” barrels due to their added accuracy from the weight.
Third, you will want to add a bipod to get the most accuracy out of your bursts. You are planning to fire a lot of rounds very quickly, so having as stable a firing platform as possible should be a priority so you can be as efficient as possible with your ammo. This is a higher priority, I would say, than a magnified optic.
Next, you may choose to get a trigger that will increase your rate of fire. This is optional. Competition triggers with a very short length of pull and short reset are a great choice due to their simplicity. I acknowledge that binary triggers and forced-reset triggers exist, and that they can be quite useful. However, they require you to “tune” your rifle a bit for them to work correctly, and you need to get used to the rhythm of your rifle so you don’t outrun the bolt. I will say that I have seen some excellent binary setups and, when tuned properly, are a great addition to the autorifle build. I have personally seen pretty reliable results out of Franklin Armory’s binary triggers.
You may also choose to invest in some high-capacity magazines to reduce the amount of reloads in a firefight, keeping the gun in action longer. Drum mags have the highest capacity, ranging from 50-100 rounds or higher, but they tend to suffer from reliability issues. Even the 75-round AKM drums are not immune to stoppages. A more reliable option is 40-round magazines, which will likely still fit in the same pouches as your 30-rounders. There are other options as well, including quad stack magazines. Whatever you use, make sure you subject it to extensive torture testing to ensure that it will work when you need it most. If it’s unreliable, throw it away and try something else.
If your team is running 5.56, your best bet is to build a rifle as described above. The US Army uses the M249 SAW, which is belt fed and likely outside of your budget, even in a semi-auto configuration ($8,000-$10,000). The USMC now uses the M27 IAR, which more closely represents what you will eventually build, as it is a piston-operated carbine with 30-round magazines and a bipod.
If you lead a team of vodka-fueled AK operators, you’ll want to get your hands on a semi-auto RPK. Failing this, any AK variant rifle can fill the autorifle role with the addition of a bipod (see the picture at the top of this article). Romanian rifles (WASR-10s, Cugirs, etc.) are excellent for this because their barrels are incredibly durable and can take a lot of abuse.
The common thread with all of these recommendations is commonality of mags and ammo with your team. After an engagement, the team leader should be able to re-distribute ammo throughout the team, which is much easier if everyone is using the same magazines and ammo. Keep your team logistics simple.
An automatic rifle is an incredible asset to any small team. However, keep in mind that by its nature, a purpose-built rapid-fire weapon will consume substantially more ammunition than a semi-auto carbine. It is up to you and your teammates to balance your mission and available resources, and decide for yourselves whether or not you should make the investment. And if you want to learn how to employ an autorifle tactically within a team or squad, come to a Support Weapons Class sometime. Check my training schedule for class dates.