Indeed, my assumption was that gun is not the main weapon not even for shelling bunkers on shore. For long range attack 8 (or 16 if 4x4containers installed) Calibrs. Gun here I see as AAD or CIWS role, or pirate surprise. AADd -higher verticala range than 76mm and 2,5 higher fire rate shall do the job.
Kalibrs are useful against countries, but in the normal routine patrol mission they are not much use... you can't get a ships captain to stop their vessel punching 400kgs of HE into its side at a million dollars a shot.
A 76.2mm gun however can be fired into the sea in front of a ship to tell that ships captain you mean business without murdering any of his crew or sinking his ship.
Of course if you want to do serious damage you still can... a few 6kg HE shells into his bridge will stop any ship.
In role of CIWS - high rate of fire is better, caliber 57mm too small? Germans lately build system based on 35mm Oerlikon guns to protect militaru camps/installations against artillery or mortar missiles ! so 57mm should deal with this as well. Of course I can be wrong and you right
Yes and no. the smaller calibre allows a very high rate of fire in a short burst so if the target turns or slows down or speeds up in the seconds between your gun firing and impact then the spread of shells means you still will likely get a hit. With heavier rounds like the 57mm guns the advantage there is guided shells so if the target turns or changes speed the round fired can manouver and compensate for that and still have a good chance of a hit/kill.
Instead of firing a 200 round burst as with Kashtan... you can get away with firing one or two rounds of 57mm shells that are guided and still have a very good probability of a hit... 57mm shells are huge but take up less space than 200 30mm cannon shells.
the thing is that a larger shell like a 76.2mm round can also be guided but will have more punch with a heavier round and greater range and altitude.
Against some larger targets the heavier shells will also be more effective.
to give you an example in Afghanistan in the 1980s the soviets found when the muj built rock piles in the mouth of caves that their rifle fire could not penetrate. 30mm grenades however blew the rock walls down and scattered the rock fragments around like extra shrapnel. the HE power of the 30mm grenades was rather more effective than smaller calibre lighter rounds.
Of course I can be wrong and you right
Just a discussion... there is no right and wrong... just opinion... which can change with new information.
The very high acceleration of the Pantsir range missiles means it really needs to be in an external turret that can be pointed at the target before the main booster fires.
the only other option would be vertical launch where the missile is blasted up into the air and gas generators (side thruster rockets) roll the missile to point in the direction of the target before the main booster rapidly accelerates the missile away.
If you do that then the gun component of the system could be a few Duet mounts and the radar and EO systems incorporated into the existing ship systems. The advantage of vertical launch is that you could also carry Morfei missiles with IIR seekers and lock on after launch capability for fire and forget capability against very short range targets along with several twin barrel gatlings.
Of course with Morfei you could replace the 30mm gatlings which are primarily for very close in self defence and use a larger calibre gun that would be useful for a range of other tasks that 30mm is not so useful for.