However, for the Air Defense Gun RFI the Pantsyr S2 on a wheeled chassis will be offered though the requirement is only for a high-fire cannon & not a combined gun/missile AAA system . That coupled with the current economic mess , am not sure if India can afford the Pantsyr S 2 and will probably opt for cheaper alternatives from Serbia or Poland. Anyways , fingers crossed .
Guns on their own lack the range to be effective... even 30mm cannon are only effective out to 4-5km at most... unless you want to go to a much heavier calibre like 40mm or 57mm calibre then most aerial targets will be able to pick off your air defence vehicles at stand off distances.
40mm and 57mm calibre weapons would lack the rate of fire to be effective against a manouvering aircraft or cruise missile like target and would only be effective in the AAG role with guided shells.
The whole reason for the Tunguska and Pantsir is to combine the advantages of both guns and missiles so they compliment each other and reduce costs.
Pantsir-S1 is not as cheap as a gun only system like Shilka, but it is not just replacing the SPAAG, it is also replacing the short range missile component, so rather than just replacing the ZSU-23-4 it also replaces both the SA-9 and the SA-13 and if you look at the specs you get a much more effective system. The guns on Pantsir-S1 have much greater range and hitting power than the 23mm cannon of the Shilka with its two twin barrel guns pumping out about 5,000rpm replacing four single barrel guns pumping out about 4,000rpm. The effective range is about 4,000m for the 30mm rounds compared with about 2,500m for the 23mm calibre rounds... in this case the 30mm are 30 x 165mm rounds and the 23mm are 23 x 152mm rounds.
The missiles on the Pantsir-S1 are SA-22 Greyhound missiles with ranges of up to 20km and altitudes of up to 15km and can hit targets down to 5m, with 8-12 missiles ready to fire depending on the model.
For SA-13 the heat seeking missiles have a range of about 5km with about a 4km ceiling and there are up to 6 missiles ready to fire.
Very simply the Pantsir-S1 offers performance much better than Shilka and much better than most other similar short range SAMs in one package without the duplication of having to buy a gun system and a missile system with different vehicles.
In other words it seems to cost more... but it actually doesn't if you want decent close in air defence capability.
If they just want a gun vehicle then a cheap option would be a Shilka with its 4 x 23mm cannon removed and replaced with a single 30mm twin barrel 2A38M cannon and a couple of Igla launchers on the turret rear.
8 MANPADS and 2,500rpm 30mm cannon fire capacity would be impressive... especially with the radar and electronics replaced with modern optics and compact radar system. (no need for long range radar when targets out to 4km for guns and 6km for missiles will be the standard mission).