All of the large caliber Japanese naval guns (8in - 18in) were capable of firing rounds that would probably best be classed as Antiair incendiaries - basically a shell that burst open at a certain range filled with hundreds of small incendiary fragments.
They were generally ineffective, and as you say were bad on the guns. Some people speculate it was improper storage of this type of ammo that made Mutsu go boom.
Source - NavWeaps (http://www.navweaps.com/Weapons/WNJAP_18-45_t94.htm)
As were most Japanese warships, the Yamato and Musashi were provided with a special anti-aircraft incendiary shrapnel shell officially designated as "3 Shiki tsûjôdan" (Common Type 3) and supposedly nicknamed "The Beehive," but this could be apocryphal. This round weighed 2,998 lbs. (1,360 kg) and was filled with 900 incendiary-filled tubes. A time fuze was used to set the desired bursting distance, usually about 1,000 meters (1,100 yards) after leaving the muzzle. These projectiles were designed to expel the incendiary tubes in a 20 degree cone extending towards the oncoming aircraft with the projectile shell itself being destroyed by a bursting charge to increase the quantity of steel splinters. The incendiary tubes ignited about half a second later and burned for five seconds at 3,000 degrees C, producing a flame approximately 5 meters (16 feet) long.
The concept behind these shells was that the ship would put up a barrage pattern through which an attacking aircraft would have to fly. However, these shells were considered by US Navy pilots to be more of a visual spectacular than an effective AA weapon.
< Message edited by JuanG -- 10/15/2009 4:58:51 AM >