A simple guide to rifle calibres


To a non-shooter, all bullets seem the same, but there are hundreds of different calibres out there. ‘Calibre’ is based on (but not always the same as) the diameter of the bullet in millimetres.

Are you choosing the right calibre for your shooting? You’ll probably get different answers from everyone you ask.

Sako Cartridges’ Aki Suvilahti fills us in on the basics of calibres and the bullets in the cartridges.

He starts by saying they come in ‘families’. “So we have the .222 family, .308 family, .30-06 family, .375 family,” he says.

To give a taste of what the knotty subject of calibres is like, Aki focuses on just the .308 family. “The parent calibre is the .308. The children are the 6.5 Creedmoor, .243 Winchester and .22-250. Each of these calibres has a different sized bullet attached. They are all made from the same tube basically, so their physical size is very similar.”

This similarity means “a lot of people get confused with the simple thing with a .308 – it’s actually the same case as a .22-250”, says Paul Childerley, a professional deer manager from the UK.

“This is very generalised simplification,” Aki says, “but if you look at them they are very – in physical size – they are very similar… but different bullet sizes and you can get different performance out of the cartridges.”

Different bullets, similar sizes: Sako .308 boxes


“It’s really interesting how flexible one case can actually go,” says Paul, “right from the .308 right down to the .22-250 and different performances.”

“Yes exactly, for example with .22-250 you are able to get really high velocity over 4,000 feet per second, and then you switch to heavier bullet in .308 and then you get a more penetrating bullet: different performance, same physical case but different bullet.”

The .308 came about as part of US testing for a new military cartridge after the Second World War. Ballisticians experimented with .300 Savage and .30-06 cases. like the .308, these are all called ‘.30 calibre’. the military cartidge that was born from this was the 7.62x51mm NATO or ‘7.62 NATO’ that was the stock NATO cartidge until the introduction of the 5.56 NATO in 19XX. Meanwhile, the Winchester ammunition company took the prototypes of this military round and developed a hunting calibre called the .308. Winchester – and that’s the .308 we know today, one of the most popular hunting cartridges in the world.

So how come ammunition manufacturer Sako make Winchester and Remington bullets?


Paul is curious about who comes up with the names for bullets. “So we’ve got Winchester, Remington, 6.5 Creedmoor all these names. Where do they come from?” he asks.

Aki explains the logic behind some of them.

“I will give you a little bit of background about calibre making itself,” he says. “So let’s take the Imperial calibre .308 Winchester (imperial because it is in inches not millimetres). .308 means groove diameter of the calibre and Winchester then itself is the inventor of the cartridge. There is no standard or standardised way for what is the later part of this calibre – the word ‘Winchester’ – sometimes it’s inventor, sometimes it’s a place.”

Other calibre names are based on a more modern ‘metric’ naming system, according to Aki, like 6.5x55SE – it’s 6.5 millimetres in diameter, 55 millimetres long and SE is Sweden’s two-letter country code. that’s why it is sometimes known as the 6.5 Swedish, which differentiates it from the 6.5 Creedmoor.

There’s something else bugging Paul.

“So how can Sako make Winchester or Remington rounds?”

“These are things that you cannot patent,” says Aki. “So when somebody invents a new calibre, it is something that of course has to be approved by the CIP (in Europe) and SAAMI (in North America), then you are required to invest in tooling, ramping up the production but you actually cannot own or patent the calibre.”

“Oh really, why?”

The reason is companies need to invest heavily in production and tooling and if for some reason they are unable to produce the specific ammunition, there would be a shortage.

Not allowing patents also gives manufacturers the freedom to create their own versions of each calibre for different purposes.

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