Double D., The 30 Pdr. Parrott Siege Rifles, (4.2 Inch) were some of the most long lived artillery of the Civil War. Virtually all of these long range rifles survived
far beyond the 1,000 round limit that Federal forces placed on the line service of cast iron guns. One 30 Pdr. used in the siege of Charleston's Fort Sumter fired
over 4,000 rounds without a problem. Hence, it was the piece chosen to convert. I've read that several of the 150 Pdr. Parrotts were also converted, because,
with the exception of the "Swamp Angel", they also were considered to be very reliable. After all, they were chosen to accompany the 11" Dahlgren Shell Guns in
Monitor Turrets, because of the lack of 15" Dahlgren availability. The Monitor Lehigh is a good example; it was in many battles and bombardments without any
problem from it's 8" Parrott Rifle.
Tracy