Yes, those are the projectiles. It would be impossible to tell which projectile came from which gun because of the camera angle , etc. I posted the photo only to illustrate the delay mechanism built into the firing circuit. The exact sequence varied between the different batteries because of things such as barrel length, distance between guns, velocity, etc. The MK 6 guns of the North Carolina may have used a center gun delay which would have been different from the Iowa Class MK 7 guns which used a left, right, center delay, according to my usually reliable Fire Control expert.
I don’t have experience of the bigger guns, they were all but out of service when I joined the RN. I do know that there was no delay on the little guns that I did use such as 4.5 inch Mark III’s, both firing together. The theory was that if one gun fired a fraction of a second before its partner the recoil slewed the turret off-line and threw the other gun out. When firing in salvo (alternating left and right guns) the elevation jump at each shot and the left and right jumps could be measured easily. In fact we used to record the servo performance to check the recovery time after each shot to be sure that it was back on line ready for the next shot. As these guns only fired a 52 pound projectile the mounting and ships structure could handle all guns together. The blast of guns of this size was significant, enough to damage minor fittings such as lights and, on aircraft carriers, to damage aircraft parked too close to the line of fire. The recoil effect was felt as a jolt, sometimes crockery in nearby messdecks suffered, not much more.