 In the flank barbettes are mounted two mark III RML 64 pounder 64 cwt guns , numbers 462 and 463 . They are rifled muzzle @-@ loading heavy guns weighing 64 long <unk> ( 3 @,@ 300 kg ) with a 6 @.@ 3 @-@ inch ( 160 mm ) calibre steel barrel . They were made to the model 's 1867 pattern by the Royal Arsenal , <unk> , England in 1872 . Their intended use was to protect the flanks and approaches to the fort . These smaller guns use an 8 lb ( 4 kg ) charge of gunpowder to send a 64 lb ( 29 kg ) <unk> up to 5 @,@ 000 yards ( 4 @,@ 600 m ) . There are iron rings fixed in the rampart wall that indicate traversing gun carriages were intended to be mounted , though this never <unk> . The guns were supplied with siege over @-@ bank carriages . The lower carriage sections are the type made for the guns when used as field pieces and the upper sections are brackets that raise the guns to the over @-@ bank firing position . In this particular configuration the two guns are thought to be the last in the world . 
