Traditionally the calibre has been dictated by the rate of fire and range/altitude.
For instance... if you want to shoot at bombers flying at above 5k altitude then you need a large calibre gun... its low rate of fire means you need a lot of them of course.
As targets got faster then you needed a high rate of fire and smaller calibre to fire enough rounds at the target while it was in range.
The problem is that while very small calibres allow enormous rates of fire, they also limit the effect on target when hits are achieved, so you need a balance between rate of fire and weight of shell.
During WWII probably the most common ground based AA vehicles in the Soviet Union were trucks with four Maxim rifle calibre machine guns mounted together, or later 12.7mm HMGs on a similar truck with one or two gun mounts generally. They did have a 37mm single barrel gun but it was not widely produced.
The 14.5mm HMG was found to be rather effective against air targets at close range... it was a smaller lighter weapon that could be easily hidden and produced in numbers, and was used on the BTR-40 in a mount intended from the start to be fully dual role AA and ground support weapons. They also mounted 14.5mm KPV HMGs on train mounts and light APCs like the BTR-60 and BRDM-2 in place of a 20mm cannon as used in the west.
The 14.5mm lacked the HE capacity of most cannon rounds but made up for that by having rather better kinetic armour penetration performance... effectively it has twice the energy of American 50 cal machine gun rounds (and 12.7mm Soviet HMG rounds too).
In fact there is a South African anti material rifle that uses a 20mm cannon round for anti personel use but also a barrel for firing 14.5mm HMG rounds for anti armour use.
They started using 57mm guns on AA gun vehicles because their standard towed AA gun was the S-60 57mm gun but the low rate of fire and lack of radar and four round clips meant new high speed enemy jets were just too difficult to engage, so they adopted the 23mm cannon in the ZSU-23-4 whose four barrels spit out 23mm cannon shells in enormous numbers and the radar gets them close enough to the target to make them very effective. Improvements in armour protection and helicopter sensors and missiles meant they replace the 23mm cannons with 30mm cannons in the early 1980s with a similar rate of fire but a heavier projectile able to take on heavier targets at greater distances.
The vehicle that is the subject of this thread has taken things full circle and gone back to the 57mm guns... but just one this time.
More precise servos, more accurate ammo, better optics, faster traverse and elevation, and new ammo types mean a new 57mm gun has become the best solution... the problem is small drones.
At 3km a 200 round burst of 30mm cannon shells would likely cover a target 20m by 20m... which is huge. The 200 shells wont be centred around the centre... they will be scattered randomly around the entire area... now if you are a fighter plane or a hovering helicopter then a random scattering of 200 shells over that area likely means 30+ direct hits at random parts of your aircraft... which is going to be lethal, so everything is fine there, but if the target is an incoming cruise missile or a hand launched drone the size of a dinner plate then that 200 round burst and the next 200 round burst that follows it will likely miss you completely... the next two 200 round bursts will likely also miss... so 800 rounds fired and the target continues on its way... that is a problem... especially as those rounds only explode when they hit something so if they don't hit then they just blow past at high speed and do nothing at all except provide a fantastic light show for the drone operator watching all those 30mm cannon shells whip past.
A proximity fuse wont help a lot because it will take up a lot of space... make each round a lot more expensive... and even then firing dozens of them they still might not get close enough to set them off.
Going to a 57mm calibre round means a lot more HE and metal fragments so airburst rounds are much more effective, and if you can devise a cheap way to set them off at a useful distance then what you couldn't do with 800 rounds of 30mm ammo you might be able to do with 2-3 rounds of 57mm ammo.
Being a bigger heavier round it retains velocity better so it will get to the target faster... and when it explodes near a target a 2kg HE charge with perhaps 3kgs of fragments means a much heavier shower of fragments much more likely to bring down aircraft targets... especially fragile little drones or cruise missiles.
For a manouvering target you can use guided shells, but they will be rather more expensive so most of the time you would use airburst rounds against air targets.
57mm rounds are also a useful solution to the problem that 30mm rounds are becoming less effective against enemy light armour... a 57mm APFSDS round could penetrate the sides of some tanks, so BMPs should be vulnerable at normal battle field distances too so it becomes a good weapon for BMPs.
Did Soviets or Russians ever make a 14.5mm gattling type weapon?
Not as far as I know... certainly nothing that made it into service. Gatling guns are for shooting at small fast targets in the air or from the air... so naval gatlings are common for shooting down Anti ship missiles, and for aircraft like the MiG-31 (23mm vs cruise missiles and fleeting shots at enemy aircraft) and Su-24 (23mm shots at ground targets flying low at near supersonic speeds), and the MiG-27 (30mm shots at ground targets while flying at high speed very low...).
They also had gatlings on their Hind helicopters (12.7mm only AFAIK) and in gun pods... rifle calibre, 12.7mm calibre, 23mm calibre and 30mm calibre...
[qutoe] I think it would have been pretty useful to take out soft skin and light armour in modern warfare today there is many mrap or armoured 4x4 and some with protection against 12.7mm although not sure if the roof would be, the 14.5mm has better penetration than 12.7mm but having a 14.5mm gattling would be a good compromise instead of using the 30mm.[/quote]
Most of their wheeled APCs had 14.5mm guns like the BTR-60/70/80 and BRDM-2, the KPV seems to be a very solid gun that was rather reliable and popular, though the BTR-80A introduced versions with 30mm guns too.
The new APC turrets for the new vehicle families seem to have Kord HMGs in 12.7mm calibre.
Of course it would depend on the mission the heli was going to do. Maybe it's possible to have a 30mm gun mounted on the side of a mi-35 and a 14.5mm gattling on the other side or chin mounted have the best of both worlds. The plus point on the 14.5mm would be weight bro g lighter and number of rounds carried more when compared to 30mm also less recoil
The current model Hinds have a chin mounted turret with the twin barrel 23mm cannon which is perhaps the best compromise... the ammo is 23 x 115mm so in terms of size it is similar to the 14.5 x 114mm ammo, but trades muzzle velocity and armour penetration for HE capacity with a much heavier and slower moving projectile. It has an excellent rate of fire which makes a gatling option pretty redundant in my opinion...
Perhaps they could do what they did with the 57mm grenade launcher and design an APFSDS round for the 23mm cannon shell, but you would need a new dual feed design because the two different rounds would have totally different trajectories and therefore also rather different points of aim so you would fire one or the other but not both together...
The connundrum for helicopters is that most of the time when they are shooting at targets with cannon they are generally shooting at soft targets that a good HE round is rather more useful against... anything with armour in close and a burst of 80mm rockets or ATGMs is generally the better solution.
Because of this their 12.7mm HMG gatlings often were loaded with duplex rounds (ie two small projectiles in a 12.7mm case so effectively instead of launching one 50 gramme projectile at ground targets it was instead launching two 20g projectiles per shot... potentially killing two people instead of just ripping one in half).
The problem with 12.7mm guns is that they are short ranged and when you can hit them... they can often hit you, so cannon with a better stand off range is best... hense the 30mm cannon step. They initially wanted 23mm cannon turret but couldn't get it to work so went for fixed guns so if they are fixed you can make them even more powerful right? Eventually they got the 23mm turret to work and went back to it because it offered so many ideals... heavy HE projectile, but small compact shell case so more ammo could be carried by weight... the smaller shell cases meant less propellent and less muzzle velocity which meant less recoil and less jumping off target during a burst. Higher rates of fire are possible because of the reduced recoil, so very high rate of fire bursts means a cluster of impacts on target at once with less recoil and similar number of carried rounds as when using a HMG gun.
The 23mm gun is actually rather better for the job than any 14.5mm calibre weapon... ironically the American 20mm cannon round is actually more like the 14.5mm round with very high velocity lighter bullets than the slow 23mm rounds, but when you get hits the 23mm creates enormous holes and lots of damage, while 14.5mm and 20mm tend to just punch through...
The new 30mm rounds as mentioned above will be good and will improve performance of existing systems on land, at sea and in the air, but in terms of AA the new 57mm rounds will be good too... I rather suspect they will keep using the 30mm for some roles like RWS for a Typhoon four wheel light attack/recon vehicle, and many APCs wont need a 57mm calibre gun anyway...
Tunguska and Pantsir will benefit with new air burst ammo perhaps using a base laser sensor that can be detonated by the vehicle that fired the round at the ideal position as it approaches the target... it would renew the effectiveness of the 30mm against small targets without making them super expensive... instead of needing to fire hundreds or thousands of rounds at small targets a few rounds can be fired and detonated near the target which will send thousands of small high speed fragments at the small targets maximising the chance of a hit without needing thousands of rounds to be fired...