Gary,

The huge Blakely's did not live up to their billing and for whatever reason never got a chance to fire against monitors. In tests the projectiles wobbled ("warbled") according to various reports. Warren Ripley's book even quotes reports that they tumbled. Considering that the bolts had a low length to width ratio, 1.6, and a blunt face, it is not surprising that they would have stability issues. Also, I've noticed in images that the rifle twist rate might have been rather low, resulting in a relatively low spin rate.

It is not clear to me that the 12.75" bolts are wrought iron, although that would have been appropriate for their intended service. Blakely in a letter stated that the bolts would definitely penetrate 4" armor, and that his calculations indicated that even the "cast-iron shells" could penetrate. The 11" turret armor of the Passaic class would be vulnerable to a 12.75" wrought iron bolt, but the shell would most likely deflect or shatter. If the bolt was cast iron rather than wrought iron then I doubt it could penetrate the turret.

The bolt would be dangerous against the 5" sides and as Henry suggests might penetrate the deck even at a very shallow angle. (The squared face is better for that than rounded ends.) As Henry says, even failing penetration, spalling would be a serious hazard. And a turret hit by a 655 pound bolt would almost certainly cause disabling damage to the turret's rotating gears.

This is not the sort of weapon that any monitor would want to have closed within half a mile of and anchored as they ordinarily did for bombardment. However, due to its extreme mass, bulk and the thick bands, I doubt the Blakely could have been aimed very effectively at the time, and that it would have had little hope of hitting small moving targets at half a mile or more. With so many reports of the projectiles wobbling or tumbling, it seems likely that the rounds would have lacked the required accuracy.

The guns were slow firing because of the difficulty of lifting the heavy projectile, and forcing it into the grooves for loading. Loading and firing took 15-20 minutes according to several officers reporting a year after the guns were received. Eventually a crew succeeded in firing once every 5 minutes for half an hour through pre-staging of projectiles on a platform, liberal use of lubricant, and filing the projectile flanges ahead of loading. This was very tiring to the crew and the grooves were prone to fouling. Elevating this monstrously heavy piece was also a problem.

Another potential problem with such large specialized guns is one that the CSA often faced with imported guns: running out of projectiles during an action. The Blakely's shipped with 60 tons of bolts. That sounds really impressive, but with each bolt weighing 655 pounds, the sum amounts to only about 200 rounds. Probably 10-20% of these would have been used in various test firing, leaving perhaps 80 rounds per gun. The CSA produced "Harding" shells for the pieces but I don't know if they could or did produce a wrought iron bolt for it. 80 rounds per gun is certainly more than enough for one or two close, lengthy, hard fought engagements, but it would discourage long range dueling.