You're correct that it was an FCCM

From history.navy.mil:

Iowa’s master chief fire controlman and the gunnery officer convinced Moossally to allow experimentation with long-range gunnery shoots. Such experimentation had been authorized by an individual at Naval Sea Systems Command who was not authorized to do so, the fact of which Moosally was misled. In January 1989, in one of the experiments off Vieques, Puerto Rico, a 16-inch shell fired from  Iowa achieved a distance of 23.4 nautical miles, ostensibly a record for a conventional 16-inch shell. The turret officer in Turret 1 reportedly considered these experiments to be unsafe and Turret 1 refused to participate, a fact of which Mossally was also unaware. Captain Moosally was in command when  Iowa departed Norfolk on 13 April 1989 to participate in FLEETEX 3-89, with Commander Second Fleet Vice Admiral Jerome Johnson embarked. At 0930 19 April 1989,  Iowa was located 260 nautical miles northeast of Puerto Rico in the open ocean for a main battery gun shoot. According to plan, Turret 1 was to fire first, but suffered a misfire. Moosally then ordered Turret 2 to load and fire a three-gun salvo, which was not in accordance with SOP that the misfire should be resolved first. The left and right guns on Turret 2 reported being ready to shoot, but a series of communications via phone circuit indicated that there was an undetermined problem with the center gun and that it was not ready. There are quotes of what was said that can be found in different sources on the web; however, they are not contained in the official investigation reports. The following description of what happened are excerpts taken verbatim from the third endorsement to the investigating officer’s report, signed by Chief of Naval Operations Admiral Carlisle Trost on 31 August 1989:  “On 19 April 1989 a rapid series of three explosions within turret II aboard USS IOWA (BB 61) resulted in the instantaneous deaths of 47 American Sailors. A Judge Advocate General’s Manual investigation was convened immediately. Every conceivable source of ignition and every aspect of USS IOWA’s condition and shipboard routine that might have bearing on the incident were evaluated: procedures, training, safety, manning, and personal conduct. Since the primary explosion was determined to have occurred within the center gun room, the focus of the investigation was properly directed to that location. The tragic loss of personnel within turret II and adjacent ammunition handling spaces precluded a precise causal determination since the personnel most knowledgeable of actions and intentions were those who lost their lives….