Prior to the Federal Government's attempt at resupply of Ft. Sumter on April 12-13, 1861 it was an unknown as to who would fire the first shot of the coming conflict, or where. Most of those of gambling inclination would have bet that the war would have started in Florida, with contest in the Pensacola area.
General Braxton Bragg had been placed in command of Confederate forces in the area and on April 6th received a communication from President Jefferson Davis. Davis offered suggestions on possible avenues of success against the Federal fortifications in Pensacola in his letter, which was penned on April 3rd.

The following refers to use of Santa Rosa Island in Pensacola Bay:
"If that first step the establishment of a mortar battery was permitted you could establish gun batteries also, and then carry forward your approaches until you were attacked."

I've found no reference of the ordnance that would have been used in this bombardment, though the mortars of Ft. Barrancas (10"Bore Model of 1858) were shipped to New Orleans apon its capture and are reported to have gone unused at Ft. St. Philip.