A History Of Infantry Firearms Calibres

Why did we end up with a calibre of 5.56 mm (and others with 5.45 or 5.82 mm)? The understanding of modern infantry firearms calibres requires in part an understanding of their history.
The typical European 18th century service long firearm was a musket. The calibres were astonishingly large, and the typical bullet was actually a spherical ball. Cartridges were introduced, typically paper with ball and blackpowder, and de-mixing of the blackpowder over time was an issue.

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Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Alexander Frye

    We ended up with the 5.56 because of McNamara’s institutin of systems analysis, and on embarrassing secret “scientific” studies, with input from smart (whiz kids) people who knew nothing of warfare.

    • S O

      This wouldn’t explain why the Russians ended up with 5.45, why the Chinese ended up with 5.8 and why NATO ended up with 2nd gen 5.56.

    • dp

      No, no “screw-up” per see happened. It was just soundly and well perceived (and received) tendency of the time. Just like hairdos and clothing; so much different now than in 60s (boy, were those girls charming). And besides, everything is subject of historical development.

    • MichaelZWilliamson

      No, we got stuck with the abortion of the M14 because the US Army insisted it knew better than the people who were already designing assault rifles (including Garand), how to design rifles.

      5.56 was designed long before McNamara came along, and the British had been pushing for .280 since the 1940s.

      Notice the Chinese and Russians went to small calibers, too.

      Nor were the post-WWII studies, “secret.” It’s a well-established fact from multiple studies by multiple militaries that the maximum range at which standard troops can reliably engage is 300m. Beyond that, hit probabilities equal that of frag from support weapons.

      And if you’re planning on using any automatic fire, the smaller cartridge is more controllable, so you don’t spray the sky. Have you ever actually fired an M14 on full auto? There’s a reason the Army locked most of them into semi only.

      Add in a greater loadout, and we have what everyone else has: Small calibers for primary issue, larger calibers for marksmen or snipers.

      • Alexander Frye

        So please tell me where your knowledge comes from? I’ve attached proof to my claims…

        5.56 MM or .223 was designed when Eugene Stoner and Armalite needed to come up with a different caliber from 7.62NATO that the AR-10 shot. It was General Willard G. Wyman that asked Stoner to do this after an AR-10 demostration. Stoner redesigned a .222 Remington round which was slightly longer and could be filled with more powder. This lightweight , but high powered ammunition led to Armalite’s new rifle dubbed the AR-15(1). So no, 5.56 was not made pre-McNamara… After the AR-15 was renamed the M-16 and accepted by the Army is when the Russians hopped on the SCHV concept.

        Actually yes, the testing for the AR-15 was conducted under the guise of national security(2). In 1962 there were lethality tests conducted on human Indian heads, human thighs and live goats. It was a 286 page record classified as “Secret.” The tests were carried out by a biophysics division with results recorded, and studied by Arthur J. Dziemian and Alfred G. Olivier.(2)

        (1) C.J. Chivers, The Gun, Simon and Schuster Paperbacks, 2010

        (2) “Report of of Task No. 13A: Test of the Armalite Rifle AR-15,” Submitted on August 20, 1962 . Declassified and on file at the National Archives.

        (3) Wound-ballistics Assessment of M-14, AR-15, and soviet AK Rifles (US Army Edgewood Arsenal), Biophysics Division, March 1964

  • Lance

    Wended up with 5.56mm and there Comie equivalents because they wanted meant o carry a lot of ammo and be able to spray a lot of bullets on full auto that’s controllable. Overall still think 7.62mm NATO was one of the best calibers to goto war with but 5.56mm can hold its own under 300 yards. Overall think 5.56mm and there AR system rifle will stay with us for a long time much as 5.45mm and AKs will stay with Russia.

    • ColaBox

      Do you edit before you post?

  • dp

    Very pertinent topic, especially in this time of development. I view the issue as versatility vs. efficiency. More of the efficiency in current small bore ammo, so much less versatility. Go back to past discussions to find out on your own.

  • 101nomad

    As a citizen, I no longer rely on what the military assigns me. The “5.56 vs 7.62” no longer matters to me in that respect. In the 60s when I was in the military, the M16, 5.56 NATO, was a disappointment even on the firing range, (we were raised on the M1, (basic training), and M14, the M14 was our rifle during almost two years of jungle warfare training in the 173rd Abn). The establishment did us no favors with the M16s. Understand they have improved greatly. I still have an aversion to even touching any of the clones, (5.56), or actual rifle/carbines of today. It is always good to have choices, I hope we will always have the right to exercise them. If you can not shoot the one you love, shoot the one you got.

    • dp

      You might be interested to hear this: at the time you served I was on the opposite side. When I heard of M16 I was very interested in it – it appealed to me purely on technical grounds and in same way still does. Since I was assigned (as a non-commission) to job of armourer, I brought the subject of my interest to senior and experience man who was also my tutor. He told me in return: “..and what is this supposed to shoot, rodents?” and then added: “rifle must nail the man on first shot “. The man was brought up on 8mm Mauser. There was no more talk on the subject since I might have been in suspicion of defending enemy’s equipment.

      • 101nomad

        For all the early hype on “the black rifle”. I really don’t think it was the rifle that “scared” anybody. The skill, discipline, and determination of the men behind the rifle was the fight. Hope you are doing well, after all these years.

    • Alexander Frye

      101nomad Today’s variant of the M-16 and M-4 rifles and carbines are the cat’s boots. They have gone through several changes from when the first two platforms came out in the 60’s. The ammunition that this platform fires has even had to go through a lot of changes as well. I love my Army issued Colt M4. A lot of OGA, and SOCOM dudes will tell you the same. Even as I speak some SOCOM units are giving up the SCAR for another variant M-16 and M-4 design.

  • cwolf

    In a sense, weapons evolve based on a modified METT-T (mission, enemy, troops, terrain-technology). The world changes. Artillery was the leading killer in WWII; small arms is the leading killer in today’s wars. Soldiers today wear IBA, are in vehicles, may use suppressors, in MOUT, etc. All of which tends to push for shorter weapons with adjustable and even folding stocks. Adding rails has revolutionized rifles; folks add lasers, lights, grips, sights, etc.

    The German WWII tactics and the then-new auto rifles and SMG impressed lots of soldiers/analysts. Full auto fire IS impressive, even if often inaccurate. Even suppressive fire, however, needs to be reasonably accurate to be effective.

    The military is by definition slow to adapt changes due to the large installed base of research, manufacturing, maintenance, and training investments/costs. Plus they are risk averse……

    Ph/Pk is far more complex than simply putting a rifle in a fixture and shooting. It is the weapon, bullet, sight, training, etc. plus other equipment interactions that drive lethality.

    All of which is why surveys don’t give you an accurate analysis. In a recent test with qualified shooters, almost nobody could hit moving targets. No surprise…. we don’t train that nor are iron peep sights the best choice for leading a running target. So when soldier X says he shot the running bad guy at 100 yards and the bad guy didn’t get knocked backwards 3 feet, how do we know what really happened?

    It is true that Army ammo has no accuracy standard and a FMJ bullet tends to ‘ice pick’ targets. The Mk262 is far more accurate and lethal. However, read the accounts of the DC sniper; at <100 yards even the FMJ does a lot of damage.

    The M14 was a great weapon for the Fulda Gap in Germany. When soldiers with M14s faced folks with AK47 in the RVN jungles, the M16 started looking pretty good. An M14 on full auto is a duck hunting weapon; it is long, heavy, and kicks.

    If you wanted to do something to improve rifle performance tomorrow, the biggest bang for your buck would be Mk262 ammo, better sights, and better training.

    But what about the 6.8 et al? It's very unlikely. None of these new calibers have been through large scale full-auto testing. The differences in effectiveness is not a big leap forward. The military would more likely go to 7.62 before it went with a brand new caliber.