Everyone wants 7.62… Until They Have to Carry It

Above: Sen. Ernst questions Secretary Mattis

By Charles Bausman

During the recent confirmation hearing for James Mattis as Secretary of Defense, Senator Joni Ernst (R) of Iowa questioned the lethality of the caliber of round currently used by U.S. military forces (5.56x45mm) primarily with the M4 carbine.

“Our military currently shoots a bullet that, as you know, is illegal for shooting small deer in nearly all states due to its lack of killing power… Do you agree that we cannot grow a more lethal force while using outdated small arms and ammunition?”

Senator Ernst did not directly request information pertaining to moving to a larger round such as the 7.62mm, but the reference seemed apparent. We requested clarification from Senator Ernst’s office but received no reply.

Secretary Mattis responded that he wasn’t currently up to date with the ongoing testing to improve the 5.56 round due to his break in service, but made no mention of moving to a 7.62 caliber round or carbine weapon system.

The 7.62 vs 5.56 argument stems back to the Vietnam War and clearly continues today, despite a plethora of testing by the Department of Defense and independent research. Complaints of lack of stopping power, barrier penetration, and reduced yaw at the outer limits of effective ranges are common. Various departments of the military have continued to improve upon 5.56x45mm round as a result of user feedback, resulting in the advent of rounds such as the Mk318 SOST and M885A1.

The Russian military, commonly known for the production and proliferation of the 7.62 AK-47, has utilized a smaller round since the 1970’s. Following research of American combat operations in Vietnam, Soviet researchers determined the ammunition carrying capacity of a 7.62 rifle was not great enough. The ammunition carrying capacity was a primary reason for the U.S. military determining that the M-14, a 7.62 rifle, did not meet the needs of troops during the early days of the Vietnam advise and assist mission.

The Soviet government initiated a project which resulted in the adoption of the AK-74, utilizing a 5.45x39mm round. The Russian military continues to use the 5.45 round in their next generation rifles, the AK-12 and A-545.

Because 5.56 vs. 7.62 ballistics debate has been so heavily covered by a multitude of researchers and internet commandos, we will focus on the realities of what a switch to the 7.62 round as the infantry rifleman’s round might look like in terms of weapons platform and performance, weight, and effect on physical performance. For the sake of comparison, we’ve chosen to focus on the M4, the MK 17 “SCAR Heavy” , and the AK-15.

(Interested in getting nerdy on ballistic comparisons? See “sources” below the article for several articles that cover the subject.)

Weapon System Comparison

M4 Carbine
The M4 is the most common weapon system employed by U.S. military forces, and serves as our baseline for comparison to other 7.62 options. An adaption of the M16, it entered service in 1994 and is the primary personal carbine used by conventional and special operations forces.

  • Weight with Loaded Magazine: 7.31 lbs
  • Max Effective Range: 500 meters
  • Magazine Capacity: 30 Rounds
  • Cartridge: 5.56x45mm NATO
  • Fully Loaded Aluminum Magazine Weight: 15.875 oz

The MK 17, also known as the Special Operations Combat Assault Rifle (SCAR) Heavy is a 7.62 weapon system developed by FN Herstal and first fielded by SOCOM units in 2007. It is currently the only 7.62 rifle in the U.S. Military not used for long range precision fires, although it can be adapted for such use.

  • Weight with Loaded Magazine: 9.56 lbs
  • Max Effective: 800 meters
  • Magazine Capacity: 20 Rounds
  • Cartridge: 7.62x51mm NATO
  • Fully Loaded Aluminum Magazine Weight: 1 lbs, 10.5 oz

First fielded by Russian forces in 2014, the AK-15 is the latest AK style rifle, to be utilized as an individual rifleman’s suite or a squad automatic weapon. The AK-15 is still undergoing testing trials with Russian operational forces, with the AK-12 (5.45mm) as it’s competitor.

  • Weight with Loaded Magazine: 9.04 lbs
  • Max Effective Range: 500 meters
  • Magazine Capacity: 30 Round Magazine or 96 Round Drum
  • Cartridge: 7.62x39mm
  • Full Loaded Aluminum Magazine Weight: 2 lbs, 11.37 oz

As the chart below displays, the weight difference between weapon systems is marginal. A SCAR-H with a fully loaded magazine of 20 rounds weighs 2.25 lbs more than the M4. Similarly, the AK-15 comes in weighing 1.73 lbs more than the M4.

In terms of general performance, the 7.62 rifles are able to reach out further on area targets, while point target max effective range is similar between the SCAR-H and M4. The SCAR-H magazine capacity is limited to 20 rounds in comparison to the M4 magazine of 30, although extended SCAR magazines are becoming commercially available.

M4 Carbine Mk 17 SCAR – H AK-15
Weight w/Loaded Magazine 7.31 lbs 9.56 lbs (+2.25 lbs compared to M4) 9.04 lbs (+1.73 lbs compared to M4)
Max Effective Range 500m Point Target

600m Area Target

500m Point Target

800m Area Target

800m Area
Magazine Capacity 30 Rounds 20 Rounds 30 Rounds
Cartridge 5.56x45mm NATO 7.62x51mm NATO 7.62x39mm

It should be noted that FN Herstal reports the SCAR-H MOA of 1-1.25. The MILSPEC for the M4 is 4.5 MOA, although it can shoot considerably better dependent on the round. We were not able to find information on the AK-15 for point targets or MOA data.

The Fighting Load and Physical Performance

Weight Comparison

Based on the normal ammunition fighting load of 180 rounds, and a magazine in the weapon, we calculated the approximate weight difference of rounds, magazines (30x rounds per), and weapon. In comparison to the weapon only weight difference, the full combat load out has a significant difference.

180 Rounds Fighting Load and Weapon with Loaded Magazine
M4 Carbine Mk 17 SCAR – H AK-15
Number of Magazines Required 6 9 6
Magazine and Ammunition Weight 5.95 lbs 14.9 lbs 16.26 lbs
Weapon Weight with Loaded Magazine 7.5 lbs 9.56 lbs 9.04 lbs
Total Weight 13.45 lbs 24.46 lbs (+ 11.01 lbs compared to M4 Fighting Load) 25.30 lbs (+ 11.85 lbs compared to M4 Fighting Load)

With the weight of fully loaded magazines equal to 180 total rounds and the weapon with magazine inserted, the SCAR-H and loadout is 11.01 lbs more than the M4. With the same variables, the AK-15 is 11.85 lbs more. While not as large of a weight gain as we expected, it is significant for an already loaded down rifleman.

The Soldiers Load and Speed

We’ve studied the effect of weight on rucking speed before, but the study’s focus was on long distance movements over varying terrain. We wanted to see what the impact of increased weight might be on short, sprinting speed starting from the ground. While nothing will replicate the demands of a maneuvering under fire, moving from micro-terrain cover to micro-terrain cover while accurately engaging your weapon system is the foundation.

We conducted a mini-study with two of our lab rats to better understand how short sprinting might be affected by increased load.

As our baseline combat load weight, we referenced a Army study “The Modern Warrior’s Combat Load” which analyzed the soldier’s load during a 2003 Afghanistan deployment.

Source: “The Modern Combat Warrior’s Combat Load”

We conducted three iterations of a 35 ft sprint, starting from the prone, with three weights. With two timers, we used the average of the three sprints at each load to determine how speed was affected.

  • Sprint #1: Unloaded
  • Sprint #2: 63 lbs (Average fighting load with M4)
  • Sprint #3: 74 lbs (Average fighting load with 11lbs weight difference between M4 and SCAR-H)
Sprint #1 Average @ Unloaded Sprint #2 Average @ 63lbs Time Increase – Sprint #1 to Sprint #2  in Percentage Sprint #3 Average @ 74lbs Time Increase – Sprint #2 to Sprint #3  in Percentage
Athlete 1 2.83 seconds 3.42 seconds +21% 3.75 seconds +9.6%
Athlete 2 2.75 seconds 3.2 seconds +16% 3.37 seconds +5%

The mini-study shows that the added weight of a 7.62 load out did have an impact on short distance sprinting. Athlete 1 increased by 9.6%, and Athlete 2 increased by 5%.

The athletes reported that they felt the weight affect their speed most while getting up from the prone position. The actual sprinting portion felt similar regardless of which load they were carrying. We would like to explore this further, as the traditional fire and movement requires the soldier to complete this motion multiple times. We would expect the percentage in time to increase as the movement was conducted repeatedly due to soldier fatigue.

If we were to increase the number of repeated prone to sprints to ten total sprints, or approximately 100 meters, repeated consecutively similar to fire and movement, the results would be more significant. The increase in load from 63lbs to 74lbs would increase the total exposure time (time spent sprinting forward) by 3.3 seconds.

We haven’t tested this yet, but would expect the time increase to be even more significant than our math, as the athlete would clearly tire and become slower with each sprint. It does not take much knowledge to understand that heavier generally means slower, but quantifying that number in relation to performance is critical for military leaders of all ranks.

The problem of the “Soldier’s Load” has existed since the earliest armies. Assyrian spearmen carried a load of up to 80 lbs. Vietnam era infantry reported loads of ranging from 80-99 lbs for extended missions. The infantryman in the Global War on Terror has maintained or increased that weight according to the “Modern Warrior’s Combat Load” study.

The U.S. Military has made significant efforts to reduce the load burden placed up soldiers, particularly infantrymen. Batteries, radios, weapons, body armor, bipods and tripods for various weapon systems have all become lighter, yet new equipment is fielded which maintains the soldier’s load at a cumbersome weight.

Overall, the results were not as dramatic on performance as expected in terms of weight increase or it’s effect on short sprinting speed, but the implications of the increasing load are significant. Follow on testing which can thoroughly analyze the specific motions associated with fire and movement, as well as additional gear requirements for 7.62 weapon systems would be beneficial.

Questions, comments, or feedback? Email coach@mtntactical.com

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