Who decided on 7.62mm calibre choice

It's always struck me that 7.62mm is an oddly specific number - wouldn't it have been an easier manufacturing choice to go for 7.5mm or even 7.7mm?

The real reason is, of course, that it was a nice, round number to start with - specifically 0.3 inch which, when all that metric stuff came along, converted to 7.62mm.

Where the “.30 inch” came from

Back in the late 1800s / early 1900s, countries like the UK were designing rifles using imperial measurements.

A .30 calibre bore became popular because it hit a sweet spot:

• Smaller than older big rounds (like .45) → lighter, faster bullets

• Still heavy enough to carry energy and range

• Manageable recoil for soldiers

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So .30 calibre stuck around as a very practical standard.

Why not make the jump to 7.0, 7.5, or 8mm when it went metric?

• 7.0 mm → smaller, lighter, faster (e.g. modern intermediate rounds)

• 7.5 mm → used by some countries (e.g. older Swiss rounds)

• 8 mm → heavier, more recoil (e.g. German Mauser)

• 
  

Each calibre reflects a different balance of:

• recoil

• range

• stopping power

• weapon weight

So once .30 calibre proved effective, there was no reason to shift slightly up or down.

1.  .303 British (late 1800s → 1950s)

Used in the iconic Lee-Enfield

Why it existed:

• Designed for long-range, massed rifle fire, think lines of soldiers, volley fire, big distances.

• 
  

What it was good at:

• Powerful

• Accurate at range

• Reliable in horrible conditions

• 
  

The catch:

• Big recoil

• Heavy ammo

• Slow rate of fire (bolt-action)

👉 Perfect for WW1/WW2 style warfare…👉 Less ideal for what came next

2. 7.62×51mm NATO (1950s → 1980s)

   
   

Adopted in the L1A1 Self-Loading Rifle (SLR)

Why the change:

• NATO wanted standardisation

• Move to semi-automatic rifles for faster follow-up shots

• 
  

What improved:

• Still powerful (basically the modern .30 calibre)

• Better for modern infantry tactics

• Semi-auto = quicker engagement

• 
  

The problem:

• Still heavy recoil

• Ammo still heavy

• Hard to control in full-auto (which is why the SLR was semi-auto only)

👉 Great for range and punch👉 Not ideal for high-volume, mobile firefights

3. 5.56×45mm NATO (1980s → today)

Introduced with the SA80 (L85)

Why the big shift:

Warfare had changed again:

• Engagements typically shorter range

• Soldiers carrying more kit

• Need for higher rate of fire

• 
  

What 5.56 brought:

• Much lighter ammo → carry more rounds

• Low recoil → easier to control

• Better for rapid, accurate bursts

• 
  

Trade-off:

• Less raw stopping power than 7.62

• More dependent on shot placement

👉 Designed for mobility, volume of fire, and modern combat realities

I've been told there is also a train of thought that whereas an SLR would be more likely to kill and take one man out the fight, the SA80 would be more likely to injure - which would take 3 or 4 men out of the fight.

But, of course, the 7.62mm never really went away.

Modern British forces still use it for:

• Sharpshooters / designated marksmen

• Machine guns

• Situations where range and punch matter more than volume

In summary

• The calibre changes reflect how wars are fought, not just technology

• 7.62 sat right in the middle - powerful, reliable, but a bit heavy for modern infantry use

• 5.56 took over for general use, but 7.62 still steps in when things need a bit more authority

Body armour changed the game

Modern soldiers are often wearing proper ballistic plates.

• 5.56 → can struggle against advanced armour at distance

• 7.62 → hits harder, better chance of defeating cover/plates

• New calibres (like 6.8) → designed specifically to punch through modern protection

Engagement distances stretched again

After years of close-range fighting (urban ops, Afghanistan compounds, etc.), armies realised:

• Not all fights are at 50–200m

• Open terrain = longer engagements again

• 
  

That exposed a weakness:

• 5.56 loses effectiveness at range

• 7.62 keeps its energy much better

Cue the return of designated marksmen with 7.62 rifles alongside standard troops.

Accuracy + optics changed everything

Modern rifles now commonly have:

• Advanced optics

• Better training

• Improved ballistics understanding

• 
  

So instead of:

It’s shifting toward:

And heavier calibres help with that. But the latest thinking is how to get 7.62mm punch without 7.62mm downsides. So even though the British Army is still centred on SA80, they are also:

• Bringing 7.62 back into prominence

• Experimenting with new calibres like 6.8

• Trying to balance weight vs power vs range all over again

And with Operation Interflex raising questions about how prepared and properly trained the British Army is for modern warfare, these are questions which need to be carefully considered - and sooner rather than later.