Consider following trains:
812023/4-HWH-PNBE JS-16 ICF coaches-2ACC,12D,2DR
22213/4-SHM-PNBE Duro-14 ICF coaches 1ACI,1ACII,4ACIII,7SL,2SLR
Above indicates that Kolkata-Patna sector is already having many trains and less number of coaches in Duronto and JS indicate that AC traffic is not very high on the sector.
Patna-Kolkata...
more... is about 530km and 8:30 hrs journey by Duronto and this train SHM-TATA-PNBE train doing 700km in 12 hr is going to be an unwanted train for HWH paxs. It would be better option to augment above trains if there is additional demand rather than introducing new train on the saturated track.
This trn is good only for TATA-Gaya PNBE paxs which shall not be enough to justify a fully ac train.