Below The Turret Ring Blog takes a look at gun caliber....the Brits might have gotten it wrong by moving to the 40mm!

via BTTR Blog.

In case of the CV90 the ammunition available at the gun varies:

• The CV9040 has a total of  24 rounds available at the gun (three rows of eight rounds) with a further 24 rounds being located in a carousel magazine used as ready racks.
• The CV9035 has a total of 70 rounds available at the gun, consisting of two belts a 35 rounds.
• The CV9030 has a total of 160 rounds available at the Bushmaster II gun.

This clearly shows the benefit of utilizing smaller calibres in combat vehicles. While the CV9040 has only 24 rounds directly available at the gun, just by using the slightly less powerful 35 x 228 milimetres calibre the amount of rounds available at the gun is nearly tripled. The 30 x 173 mm calibre still more than doubles the ready ammunition compared to the 35 mm calibre! Given that the 40 mm Bofors gun currently does not offer more armor penetration possibilities, the Bofors compares unfavourably to the Bushmaster guns. While the actual armor penetration of the 40 mm Bofors with APFSDS ammunition is higher, the added armor penetration does not allow engaging heavier armored targets: all three claibres can defeat current generation IFVs frontally and MBTs from the side - the only advantage gained by the larger calibres is additional ranges, which only matters under limited circumstances.  

"Stowed Kills".  That's the mantra of MANY armor bubbas.  They don't give a rats ass about the caliber of the gun as long as it can kill the targets it was designed for.  Additionally the number of targets that they're able to kill before having to resupply is important.

So with the idea that the 30mm can engage and kill almost anything short of a MBT (and many IFVs carry missiles to take care of those encounters) did it make sense for the Brits to move to the 40mm cannon?

Not after reading this article.

I think we're seeing a case of image over substance with the cry for standardizing on 40mm.  The juice is not worth the squeeze.