6.25mm British?

I know of the .280 based round, but did anything ever happen as far as the intended production version that was supposed to have a narrower and somewhat longer shell casing? I know that at least some mock ups got made, but did it even make it to being test fired before the 4.85mm program took over? Just looking for information and images if any are known to exist.

The 6.25mm cartridge was only ever a test platform case to try different loadings and bullets, what would you like to know I have a few photos of cartridges, cases and bullets if you would like them. In essence it was just a 280/30 case necked down to 6.25 but from what I have read they were all new production cases for this experiment.


i will interessed if exist cases of other material than brass (for this 6.25mm)

I’ve seen or heard references to a 6.25x46mm round, though I think they were only mock ups/proof of concept models.

Here’s what one looks like, numbers on the case are mine, nothing extra factory but the red blob of paint on the base. Had one of these in an all brass dummy, only other major variation I can think of without looking in one of Peters books.
6.25x43 hs

This is an extract from my history of Assault Rifles web article:

An instructive series of experiments took place in the UK in the late 1960s, when a thorough attempt was made to design an ideal military rifle round. This started with calculations of the bullet energy required to inflict a disabling wound on soldiers with various levels of protection. The energy varied depending on the calibre, as a larger calibre required more energy to push it through armour. For example, it was calculated that while a 7.62 mm bullet would need 700 J to penetrate contemporary helmets and body armour, a 7 mm would require 650 J, a 6.25 mm 580 J, a 5.5 mm 500 J and a 4.5 mm 320 J (this last figure should probably be 420 J). These figures applied at the target; muzzle energies would clearly have to be much higher, depending on the required range and the ballistic characteristics of the bullet.

A range of “optimum solutions” for ballistics at different calibres was produced. These resulted in MEs ranging from 825 J in 4.5 mm to 2,470 J in 7 mm. More work led to a preferred solution; a 6.25 mm calibre with a bullet of 6.48 g at 817 m/s (100 grains at 2,680 fps), for an ME of 2,160 J. The old 7 mm EM-2 case was necked down to 6.25 mm for live firing experiments, although had the calibre been adopted a longer and slimmer case would have been used. Tests revealed that the 6.25 mm cartridge matched the 7.62 mm NATO in penetration out to 600 m and remained effective for a considerably longer distance, while producing recoil closer to the 5.56 mm.

I believe it is correct that there were only a few dummies made of the optimised-case 6.25 mm, and I’m not sure if they were definitive. The late Tony Edwards had at least one, I believe. I included a photo of one - I slotted it into the group shot on the front page of my website. It’s the 7th round from the left, in between the usual 6.25 x 43 and the 6 x 45 SAW.

Nice Tony, somehow I missed hearing about or didn’t remember hearing about a 6.26x46.

The 6.25 trials in the early 70’s were 6.25 x 43 I have not heard of a 6.25 x 46 either, can someone shed any light on this Calibre/Experimental cartridge.


There was never any intention to adopt the 6.25 x 43, that round was made for load development and testing, because the ammo could be made easily from 7 x 43 and an EM-2 could be rebarrelled easily too.

The 6.25 x 43 case was too big and the wrong shape to be optimal for the new round, so the 6.25 x 46 was designed to be the definitive shape. I am fairly sure that they never made any shooting ammo in 6.25 x 46, the project was stopped before they got that far.