Modern small arms calibres

Some light food for a change...

I published an article about rifle calibre effects (mostly wound ballistics) at Steve's Firearm blog several days ago. The topic seemed to be more appropriate there than here.
Check it out, it's a myth-busting article meant to clean up the mess of misleading anecdotes, scientific mistakes and sentimental influences that surround the rifle calibre debate.

Rifle calibres have been discussed and changed since we moved from musket ball to rifle bullets in the 19th century. The introduction of modern smokeless propellants brought another huge boost for calibre discussions, again toward smaller calibres. The final push toward smaller calibres (calibres smaller than 7mm were already tested at the beginning of the 20th century) came after WW2 when almost every soldier got a fully automatic weapon.
The high ammunition consumption of automatic fire and issues with strong recoil (controllability of bursts and full auto fire) spoke in favour of small calibres.

Calibres around 7mm (at least 6mm) were discussed in many studies and by many commissions as ideal infantry calibres, and the British developed the good .280British rifle cartridge. NATO selected the 7.62NATO calibre due to U.S. lobbying.

The USA didn't use 7.62NATO much as assault rifle calibre - the M14 quickly got its successor in the M16 after only a few years of use as standard rifle. 7.62 was a widespread calibre for assault rifles in other NATO countries (Germany replaced the 7.62NATO G3 rifle only in the 90's) and is still the most wide-spread calibre for medium/universal machine guns.

5.56NATO, the new standard for assault rifles since the 80's, was a mixed blessing; less penetration of cover/armour, less wound ballistic potential, inferior external ballistics for long-range shots - the advantages of reduced recoil, volume and weight were only part of a trade-off that hurts elsewhere.

A good bullet design can improve wound ballistics in both calibres (7.62NATO isn't always as great as its reputation) and heavy bullets can improve cover penetration (an issue for 5.56NATO). That's probably not enough. It's reasonable to expect more than 5.56NATO can deliver while 7.62NATO as standard cartridge like in the 50's and 60's would be extremely heavy and require strict fire discipline to get the job done with the little ammo that can be carried.

I see two possible approaches to solve the dilemma.

A) Standard infantry calibre:
A common cartridge in the 6-7mm range with intermediate characteristics and modern bullet designs. This cartridge could meet the requirements for carbine/PDW, scoped rifle (squad sharpshooter) and light machine guns. The effect would be satisfactory, the weight+volume would be acceptable and the range would suffice for everything except vehicle-mounted weapons and dedicated snipers.
A single small arms calibre for the whole quad/platoon would simplify ammunition logistics very much even though different, exchangeable cartridge versions (ball, AP, tracer, IR tracer) would be used.

B) New mix of 5.56NATO and 7.62NATO:
Well-designed bullet designs are necessary to exploit both calibre's potential, and could fit different roles.
5.56NATO: PDW/carbine, light machine gun (bipod, squad-level support)
7.62NATO: scoped rifles, medium machine guns (tripod, platoon-level support)

It's not really necessary that all weapons reach out to 600m effectively. Carbines won't be very useful at that distance anyway and light machine guns put a premium on low weight for the machine gunner's battlefield agility. Small bullets can suppress almost as well as heavy ones - a strong advantage when you need to carry so much ammunition.
Medium machine guns - well, almost nobody accepts 5.56NATO as a medium machine gun calibre; the effective range and cover penetration simply doesn't match the expectations.

Finally, the soldier's dearest weapon: The battle rifle / assault rifle - the supposed "standard" firearm.

Decent marksmanship training, the ammunition consumption problem, improved sights and the experience against ill-trained spray & pray troops has led to an emphasis on the aimed single shot even more than before and even at rather close ranges. This emphasis was typical of the British army with its semi-automatic-only L1A1 (FAL) rifles in the 60's and 70's.
The preference for single shots (semi automatic fire in practice) saves ammunition and is a critical enabler for a possible return to 7.62NATO.

It's not necessary that every soldier in a squad/platoon has a weapon that penetrates common cover (walls, trees), it should suffice if a quarter or third has this capability - that's an opportunity for weight & volume savings.

Let's compare 7.62NATO battle rifles in contrast to 5.56NATO examples.

Pro 7.62NATO:
- better range
- better cover penetration
- better armour penetration
- better wound ballistics
Contra 7.62 NATO:
- heavier weapon
- fewer cartridges for same ammunition weight/volume
- a bit less controllable on full automatic fire
(designs with shoulder stock and barrel in one line like SCAR-H should be much more controllable than the older G3 and FAL designs). Such straight designs need a sight line high above the barrel - that's ideally suited to the modern rifle sights, but it was a drawback at the time of iron sights.

Other pro/contra arguments exist, but are much weaker than these (in my opinion).

The introduction of quality optical sights on non-sniper rifles (with up to 4x optical magnification) almost turns ordinary riflemen into squad sharpshooters and a few weeks of training can complete that evolution.
This turns the ordinary rifleman into a soldier who appreciates the advantages of 7.62NATO more than before - and might make 7.62NATO a great rifleman calibre.

That's a bit ironic and sad because the British went away from the single shot/7.62NATO design some decades ago after getting the universal infantry calibre issue right even earlier. The Germans turned away from the 7.62NATO as assault rifle and light machine gun calibre about fifteen years ago after playing around with the mislead and extreme G11 rifle design and its caseless 4.73mm cartridge.
Finally, the Turks are in the process of turning away from 7.62NATO, their army (biggest in NATO) will replace the G3 (7.62NATO) with half a million 5.56NATO HK416 ("Mehmetçik-1") in the next few years.

The French are the next who will reform their small arms inventory; their FAMAS F1 assault rifle still uses the first generation 5.56mmx45 cartridge, predecessor of 5.56NATO (FAMAS G2 uses 5.56NATO, but the French Army has held off a large scale purchase of the G2 so far).

The standardization of small arms calibres seems to be a mess in the NATO.
It's important to keep in mind that the optimum calibre or calibre mix depends on circumstances that change over time. A mix of 5.56NATO and 7.62NATO can satisfy, but we should consider a return to the 7.62NATO battle rifle if we aren't willing to introduce a universal infantry cartridge of 6-7mm calibre.


  1. One down side it seems to me with a new perfect cartridge. Is that it would make the surrounding cartridge seem out of place. Is the .308 enough of a step up from a 6.perfect to warrant carrying it? Would some non-combative troops find out that 6.perfect is too much gun? It might be a better cartridge, but I think it would have a disruptive on the scheme of arms.

  2. An unitary cartridge for infantry could replace 5.56 and 7.62 in dismounted applications, a unitary cartridge for vehicles could replace 7.62 and 12.7 in mounted applications.

    I consider a smart mix of 5.56/7.62 acceptable, and two unitary cartridges as superior in performance (but inferior in costs).

  3. A well composed piece on this issue, well done!


  4. I've often thought a 7mm-range cartridge like the 6.8mm Remington SPC would be a great replacement for both 5.56 and 7.62. It seems to combine many of the benefits of each caliber while sacrificing only a little of the smaller cartridge's light weight or the larger cartridge's range and hitting power.

    Of course, as you say, a separate cartridge would be needed for dedicated sniper rifles, but we already seem to be moving in that direction with the .338 Lapua, and even 7.62x51mm sniper rifles tend to use non-standard cartridges for maximum range and accuracy.

    One question, though, if we're going to also standardize on a single cartridge for vehicles, is there any reason not to use the 12.7mm Browning? The lightest vehicle mounts couldn't handle it but our 7mm cartridge might be still be adequate in those roles, and for most vehicles, the 12.7mm cartridge is already widely available and well-proven in countless wars.

    1. 12.7 mm ammo is extremely bulky compared to more rifle-like cartridges, and anything that withstands a .338 is likely built to stop 12.7 mm bullets as well.
      Furthermore, one could use a 20 mm or a low power 30 mm gun instead of a typical 12.7 mm gun.