When equipping that base unit of infantry, the squad, with automatic weapons for support fires, there are two schools of thought. These are the magazine-fed ‘automatic rifle’ vs. the belt-fed ‘light machine gun’. In World War 2 terms, this might be seen as the BAR/Bren vs the MG-42. We can see the same question being asked today, with the US Marine Corps using the M27 IAR, and the US Army using the M249. Let’s look at these options.

First, the M249. Made by FN, this is a belt-fed weapon. Unlike the M240, the M249 is chambered for the same 5.56×45 mm round as the squad’s M4s. It is also generally considered to be operable by one man. No assistant gunner required. It has a quick-change barrel to facilitate sustained fire and help deal with heat buildup. It can be operated from 100 or 200 round belts. It weighs 17 lbs empty and 24 lbs loaded with a 200 round belt in a plastic box (sans optics). It has an integral bipod, and is most effective when fired from the prone position with the bipod for stability and support.

Second, the M27. Made by HK, this is a magazine-fed weapon. It is also intended to be operated by one man. While it has a relatively heavy barrel profile, it lacks a quick change barrel. It can only be loaded with standard detachable box magazines. While there are some higher capacity magazines on the market¹, the US Marines currently only issue the standard 30 round box magazines. These are the same as what the rest of the squad uses for their M4s, so there’s some commonality there. Weight is 7.9 lbs empty, and a bit less than 9 lbs loaded with a 30 round box magazine (again, sans optics or other accessories).

Note that both weapons fire the same 5.56 mm round. So effective range and lethality are roughly equivalent. Specifics will depend on the skill of the shooter and the round being fired. I will not discuss this further.

It is also true that the M249 has a greater capacity for sustained fire than the M27. Even the M27’s proponents agree there.

A more useful question is “Is the greater suppressive capability of the M249 outweighed by what you give up?” The M27 is less than half the weight of the M249 (even after we add appropriate optics and other accessories to each weapon). The M27 is a more accurate weapon than the M249. The M27 can be used in a stack for room clearing, whereas the M249 cannot due to safety concerns stemming from its open bolt mechanism and the bulk of the weapon. Weight and bulk also means that the M249 gunner is harder pressed to keep up with the other members of his squad.

Let’s also briefly talk ammo weight. The basic load of a SAW gunner is 1,000 rounds, or five 200 round boxes, which comes out to about 35 lbs. It takes thirty four 30 round magazines to get about the same number of rounds,² and that weighs about 34 pounds. Note that by-the-book loads for the M27 IAR gunners in a USMC squad vary from 16 to 21 magazines (480-630 rounds). Variance due to the weapon being new, and TTPs being worked out. That’s 16-21 lbs of ammo. This neatly side steps the question of weight of the spare barrel assembly for the M249, but I can’t find its weight. Assume several more pounds of weight for the barrel assembly, if it is carried. If it is not carried, then the quick-change barrel feature is not useable, and sustainable rates of fire will be lower. However, they will still be significantly higher than those of the M27.

There’s also a temptation we should avoid when considering infantry tactics. While it is easiest to ponder loadouts one organizational level at a time and build from the smaller levels to the bigger ones, we should remember that the smaller ones don’t fight alone. A squad is not going to be running around the battlefield on its own. Ad hoc room-clearing units can be assembled from the manpower from a few squads in a platoon without difficulty. If flexibility is desired, additional carbines can be stowed aboard the squad’s organic transport.³ We have lots of assault rifles already, which look an awful lot like the automatic rifles in question.

The most important matter, whether the greater sustained fire rate of the M249 means it is a more effective suppression weapon than the M27, is not something I have the means to test. I would question most tests of suppression on the grounds of failing to adequately simulate combat. Setting aside the intangibles, not having a belt-fed weapon in the squad does not have a good historical record for staying power. Let’s review it:

• In World War 2, the US Army and US Marine Corps both had BARs as their squad-level automatic weapon. They considered a new Automatic Rifle version of the M14, but declined, and switched to the belt-fed M60 (and later the M249).
• In World War 2, the British Army had the Bren gun, which is also more or less an automatic rifle, being fed from a magazine. The replacement for the Bren Gun was the L7, which is a licensed version of the FN MAG.⁴
• In the 1980s, the British attempted to put a new 5.56 mm automatic rifle, the L86, into service to compliment their new 5.56 mm assault rifle. Caliber commonality. They were dissatisfied with the loss of firepower in the squad, and switched to using the FN Minimi as the squad automatic weapon.
• The Germans had plenty of experience fighting American troops equipped with BARs in World War 2. The German soldiers were armed with the MG42. The American soldiers wanted MG42s instead of their BARs. The German soldiers agreed with them. They did not think the grass was greener on the other side of the fence, and stuck with the MG42 (rechambered for 7.62×51 mm NATO as the MG3).
• The Russians built a belt-fed 7.62×39 mm machine gun, the RPD, to compliment the AK-47. It lacked a quick-change barrel, and proved to be unsatisfactory. They replaced it with the RPK, an automatic rifle version of the AK-47. They stuck with it through the caliber change to 5.45×39 mm. The Russians are very doctrinally disciplined. Once the Russians hit actual combat in Afghanistan, again the automatic rifle proved unsatisfactory and soldiers exchanged their RPK-74s for belt-fed PKMs (chambered in 7.62x54R mm). This happened again in combat in Chechnya. The belt-fed weapon was favored over the magazine-fed weapon for support purposes, even though it was heavier and bulkier. Russia is moving (albeit slowly, for want of money) towards equipping mechanized forces with PKP machine guns as squad support weapons. In the meantime, the PKM sees lots of service in that role.

There is a clear trend towards real combat driving the use and purchase of belt-fed weapons at the squad level. The US Marine Corps is bucking the historical trend, which gives me pause. The US Marine Corps tends to favor large, 13-man squads, and doesn’t fight mechanized. This might influence their decision somehow. The US Army, which uses 9 man squads (more similar to other powers at present), and does fight mechanized, has not followed the Corps in switching out M249s for M27s. Given the firepower and limited dismount capacity of the M2 Bradley, this switch would seem attractive for them. Perhaps they don’t agree with the conclusion of the USMC tests which said the M27 was better at suppression.

Without knowing the details, I could not possibly comment on the tests. Offhand, we’d want to make sure we weren’t favoring the M27s in test parameters, or putting new M27s against old, well-used, and worn-out M249s.

Here the Corps and I part ways. I much prefer a belt-fed machine gun or two at the squad level. Given the choice between the M27 and the M249 to support a squad, I’ll take the M249 every time. Belts all the way. Sometimes heavy is best.

1.) Magpul makes a 40 round box and a 60 round drum magazine, and Surefire makes a 60 round and a 100 round quad-stack box magazine. There are a bunch of others, but these come to mind first for being quality. That said, when the M27 was adopted, the USMC did not find any existing 100 round magazines to be reliable. I am unsure of their test protocol or which magazines were tested (or if 40/50/60 round magazines were considered).
2.) This works out to 1,020 rounds, but mais n’enculons pas des mouches.
3.) Admittedly I’m a big fan of mechanized infantry, but is there any army worth talking about that doesn’t provide some form of motorized transport for its infantry units?
4.) The American M240 is also a licensed FN MAG.