If it was 23mm then 30mm now 57mm, you can go directly for a 100mm antiaircraft gun without doing the 57mm. In tandem with the pantsir's 30 mm guns it will be more effective than 57mm.
If we look at WWII tank based anti armour guns... at the start they were 37mm, 45mm and 50mm and even 57mm calibre guns but then they went from a dedicated high velocity smaller calibre gun to a multi purpose larger calibre with a good HE round as well in the 76.2mm guns.
They could have jumped straight to 152mm guns but the weight and recoil and other issues with such a calibre like lack of ammo storage space meant going to 76.2mm or 85mm or 90mm made more sense at the time.
They could go for a 125mm gun that can kill enemy MBTs but a smaller lighter gun makes more sense for now.
No this is not right. I said that I would try for the 57-4 configuration the current platforms in the weight class of the 2S3 and 2S5. Of course the Kurganets and Bumerang platforms meet the current requirements for safety of the crew, even better than the BMD-4M platform, and it surely being mechanically stronger than the platform used for the 2S3 and 2S5.
I don't think there will be a 152mm calibre Kurganets or Boomerang. We have seen a 152n gun armed Coalition based on the armata chassis and I suspect the 152mm gun armed vehicle for the lighter vehicle units will be truck based but using an engine from the lighter vehicle units... Kurganets and Boomerang are similar weights and likely share an engine family that will also be used in the truck based 152mm artillery gun used to support that unit.
We do not know the rate of fire of the new 57mm gun, but there is something clear: We can not be talking about the ZSU-57-2, a weapon which production finished in 1960 like if it would be the state of the art on rate of fire and stabilisation for this caliber.
No we don't know the rate of fire of the new gun, but we do know it will likely have an automated ammo feed system as opposed to large heavy four round clips as used on the ZSU-57-2 and S-60 AAG.
Rate of fire will likely be in the 120-200 rpm range I suspect, which is plenty for guided shells and totally inadequate for even a 4 barrel battery.
The ZSU-23-4 replaced the ZSU-57-2 thanks to have better rate of fire, but more importantly still, because then the 23mm ammunition was able to make damage to the aircrafts at the time.
The ZSU-57-2 replaced the 37mm calibre AAG from WWII and improved its performance with longer range and more powerful ammo that was rather devastating if you could get a hit.
The problem was that with very fast targets getting that hit was rather unlikely without radar guidance and fast turning turrets and launching a lot of rounds very rapidly in the direction of the target... the 23mm weapons were vastly superior in that they could put up a wall of shells rapidly in a short burst at a small fast moving target. The 30mm replaced the 23mm because it could fire at a higher rate with heavier more powerful rounds that reached to a greater effective range.
Without guided shells the 57mm would not be replacing the 30mm in air defence roles.
In the anti IFV role the 57mm is replacing the 30mm cannon shell because the latter has become much less effective in penetrating enemy armour.
It is the unique combination of armour penetration performance in the anti IFV role and with guided shells the ability to hit airborne targets effectively with a few shots that makes it also effective in the anti aircraft role too that makes the 57mm round a useful new round.
For anti armour use and anti aircraft use however high rate of fire is not desirable or particularly useful.
It would only be useful in using unguided rounds against air targets... and for that role even 20 barrels would not put up enough ammo to make it viable as an anti aircraft gun with unguided shells. With guided shells just one barrel makes the most sense in terms of cost and complexity and onboard ready to fire ammo etc etc.
If we talk about a successor of this weapon, it must have rate of fire to create enough density of fire and also must have enough caliber to make damage to the aircrafts. For it, the new 57mm gun would not need to reach the same rate of fire of the ZSU-23-4 in a 57-4 configuration, but would need to surpass clearly to the ZSU-57-2. And this is fairly possible, because the ZSU-57-2 technologically is a weapon of the 1950s.
With guided shells a much lower rate of fire of even the ZSU-57-2 would be more than effective. Just having one gun means traverse and elevation can be made faster and more accurate and recoil during firing will be rather less too and the internal ammo delivery mechanism will be able to hold more ammo for the one gun, instead of the complexity of trying to feed four separate guns.