I did read your post.

The cropped area shows that the new kid is somewhat longer than the oldie - not significantly so, but at least one crimp length.

How long is that crimp? Some 10 mm? If so, then it's more likely a typo in Jane's.

If the crimp is some 30 mm long, then it wasn't a typo, and the design evolved since its last public appearance.

As time passes I find medium caliber AP more and more as a industrial solution searching for an actual military problem.

I mean, what is the probability of fighting between armed with such cannons? without MBT armed with 120mm guns?

How a super-uber-shot can be operationally justified if there are enough ATGM? I mean, ATGMs have more penetration capabilities, are guided, have greater range, some of them have NLOS capabilities, can be used dismounted in a less conspicuous way...

Indeed, I think that AHEAD/Air Burst ammunition is a more urgent need by far. a broad variety of drone / uavs are emerging as a very serious menace for armored vehicles, non-armored vehicles and dismounted infantry. Although 40mm HV grenade launcher with AB payloads are a stopgap solution, MAYBE 35mm or 40mm cannon with AB ammunition would offer enough advantages (speed and range) against drones in order to justify its adquisition. but I cannot see the actual need for armor-piercing, fin-stabilized, discarding-sabot 50mm ammunition

I think it's  case of better to have and not need, than need and not have.

Also, might this overwhelm APSs so ATGMs can do their job?

I do agree with you regarding AP.

An added bonus to increased AP performance, these necked out 40 / 50 also have much heavier HE shells, so I think that, in the end, it's all good anyway.

But I mean, against which probable adversary or target? I try to insert these concepts in the real world and in actual clashes. 

It's like sabretooth tigers. They have magnificent killing tools, but when megafauna mostly disappear, such sabres were useless. Or dreadnaught run: guns of increasingly more calibre and more and more armour. And suddenly, war ecosystem change and they were useless

What I try to illustrate are actual necessities or lack of them. Western armies need multiple layers of defensive resources against all kind of UAVs and their weapons. The threat is very, very real

Against which adversaries are going to be used such AP medium calibre guns and AP ammo? What is the probability of a clash in which a medium calibre gun is going to be enough decissive? Is there any fact-based reason for increasing calibres beyond "russian threat and their new 57mm turrets"?

renatohm said:

If the crimp is some 30 mm long, 

which it clearly is not.

Compare the difference in case length to the diameter of the 30mm projectiles: it’s significantly less.

Perhaps the US Army likes the idea of IFVs being able to penetrate opposing IFV frontal armour, has heard of this thing called APS and prefers to have more than 4 stowed kills.

DavidPawley said:

renatohm said: If the crimp is some 30 mm long,  which it clearly is not. Compare the difference in case length to the diameter of the 30mm projectiles: it’s significantly less.

I have received a slightly better version of the image, taken by Greg Knowles. I don't know how to show it full-sized (the forum software seems to shrink every image), but the designation on the S40 label says "40 x 180".

Maybe you could upload it to Google Photos or something and share the link with us?

Try it here: http://www.bocn.co.uk/vbforum/attachment.php?attachmentid=166187&d=1609620476