You are correct, 14,5 mm round is smaller than 30 mm round, and 500 14,5 mm rounds take less space than 500 30mm rounds. But if in both cases you have 500 rounds, than it is better to have 30 mm, which give you better firepower. I think difference in space they could get in two pylons, which hold a gun.
My thinking is that the 14.5mm turret version could possibly fit the 500 x 14.5mm rounds and the 2000 rounds of 7.62mm round with the PKT machine gun inside the turret area which will free up the area below the turret for the seat for the operator and perhaps a few missiles lying on the floor.
So the difference will be 14.5mm gun and space for perhaps another two Igla missiles, or extra range of the 30mm gun but less space for Igla missiles.
The 30mm round is clearly superior in performance against aircraft and armour, but this vehicle will be tasked with air defence and will be operating with vehicles carrying ATGMs and 30mm cannons and 100mm rifled guns and 120mm mortars and 125mm gun armed light tanks. I think the lighter gun for close in self defence makes more sense, and in actual terms I think the 2-2.5km range against aircraft and light ground targets for the 14.5mm gun is enough for defence while reloading missiles which will be the primary weapons.
I think this is only logical placement for missiles. Active missiles on sides of turret and spare missiles inside vehicle. I was thinking you mean placing spare missiles inside turret, where gunner sit, but there is no room for them, one man turret doesn't have enough space.
I also am thinking that by removing the 30mm grenade launcher and by using the 14.5mm gun instead of the 30mm cannon the ammo can be reduced to a level where it fills the turret area with just the single persons position below the turret ring. This would allow internal Iglas to take some of the room under the turret ring for more internal storage. In the 120mm NONA vehicle it stores something like 60 x 120mm mortar shells.
These are very small compact vehicles which is why I think the extended chassis troop transport chassis could be used for more internal storage space for missiles.
I personally doubt, that jets will fly that low and near to get into range of 30 mm gun. If they will, that pilots are doing something wrong. Helicopters are other story, when they could come very close and pop up inside range of gun, specially in more forest terrain and with hills and mountains. They could be in cover behind the mask and come very close and radars could not see them. I think for quick reaction in that close range gun is better than missile, specially if there are also bushes and trees.
There are still some jets that fly low and fast like the Su-24 and F-15E on some strike missions and with advanced warning and cueing from the AD network this system should be quite effective.
If the turret of the BTR-80A is too big or takes up too much internal space then the same turret used on the Strelets on the MTLB could easily be used too, though it has no gun armament.
There will also likely be UAVs and CAS types that this system will be effective against too.
The vehicle for Sprut-SD? Interesting option, for sure, but I don't know a lot about Morfei. When we know more about it, we could easier say if this is real option for that kind of vehicle.
It is supposed to be a unified short range AAM/SAM with IIR guidance and lock on after launch capacity. In the naval and land based system (shared with Vityaz) it is going to perform a role similar to SEA RAM except with the lock on after launch capacity it can be vertically launched (or launched from a weapon bay on an aircraft) with inertial navigation directing it towards the incoming threat. When it faces the threat it will look at all the potential targets based on their IR signature and compare them with threats in a threat library. If it was launched at a Harpoon missile for example that is 10km away but as it flys out it detects an F-22 it might pass that info back to the launch platform and allow the operator to select a new higher priority target, or continue against the targeted threat.
The threat library and the 3D thermal signatures in those libraries are already being used in auto trackers with thermal sighted systems. Older systems processed the video image to detect distinct objects like the night camera on a police helo following a suspect at night... often a box will appear around the target and that box can be locked so the operator can let the system automatically track the target rather than having to follow them themselves. The signature library is the next step and is for weapons to allow them to find their own targets.
A modern example is Brimstone which uses MMW radar signatures to find potential targets in enemy territory.
An older example was Granit which would be fired in large formations of 12 or more where one missile would climb to 300m or so and to a single radar scan of the target area. It would then drop down and analyse the radar return and determine which targets were visible and it would then assign priorities and determine which missile would engage which targets with the carriers getting more missiles targeting them. It would then transmit the target picture to the other missiles and pass on which missile was attacking which target. Later models also sent via satellite datalink the missiles radar scan of the target area, which would be useful for targeting follow up shots.
The carrier group would detect one radar scan but then the missile would drop down below the radar horizon. A bit of datalink radio traffic for a few seconds and then the next thing the carrier group would see is a dozen or more enormous supersonic antiship missiles coming over the horizon at High speed not using their radars till they were very close as a final check they were on target.