Fort Pitt, and Seyfert, McManus & Co. foundries between 1864 and 1872 . The new XV-inch gun was lengthened 16 inches so that the muzzle was flush with the outside of the turret when fired, eliminating the need for the smoke-box, Carried on later Canonicus-class monitors. XX-inch XX-inch Dahlgren shell gun: four were cast by the Fort Pitt Foundry between 1864 and 1867 as part of the original planned armament for . Three of these, named 'Satan', 'Lucifer' and 'Moloch' were accepted by the U.S. Navy, but saw no service. The fourth gun, named 'Beelzebub' was sold to Peru, where it became part of the defenses of Callao. Dahlgren shell guns and Rodman casting The navy's demand for 15-inch guns to defeat the new Confederate ironclads placed Dahlgren in a dilemma. All of his earlier shell guns had been cast solid, then had the bore drilled out—the traditional way to make artillery. Dahlgren's efforts with the XIII-inch shell gun were unsatisfactory and it was not clear that he could solid cast a 15-inch gun. However 15-inch guns had been successfully cast using the hollow casting technique developed by Thomas Jackson Rodman. In his method the gun was cast around a pipe. As the casting cooled, a smaller pipe was inserted into the first and water was pumped through the small pipe. At the same time hot coals were placed against the outside of the casting. This caused the casting to cool slowly from the inside out. As the outer parts of the casting cooled, they compressed the already cooled inner parts, making a stronger gun. The Bureau of Ordnance ordered that the Dahlgren XV-inch and XX-inch shell guns be cast using the Rodman hollow casting method. This use of Rodman hollow casting with a Dahlgren designed gun led to friction between Dahlgren and the Bureau of Ordnance, as well as some confusion in nomenclature. Table of Dahlgren shell and related guns Estimated values are indicated by an asterisk. Estimates by , except for the estimate of the overall length of the X-inch (heavy) which is based on a bore length of 117.75 inches and the estimate of the weight of the XX-inch shell which is based on the weight of the shell for the Columbiad, Seacoast, 20-inch, Model 1864. Dahlgren rifled guns Dahlgren designed several rifled muzzle-loading cannon, as well. Twenty-pounder rifle: an entirely bronze gun that was popular and