Nice work Andy. A few years ago I did some research on this to help someone writing a book on the Arkansas. Your depiction of the how the system was bolted is generally correct. The forward slanted casemate wall was laid vertically, the longitudinal runs along the casemate were horizontal. A big problem with Arkansas is that her iron came from several sources. About 400 pre-drilled used rails were collected at Memphis from stocks intended for extending the westward rail line in Arkansas. The rail weight you cite is more consistant to siding rail of the period which tended to run about 50-56 lbs/yd. As rolling stock became heavier and more cars added to the trains, heavier rail of about 62 lbs/yd became more common. The pre-drilled iron went up the Yazoo with Arkansas, but sank aboard a barge. One of Brown's first tasks was to bring up this iron. We know that more iron arrived via a rail station about 25 miles from Yazoo City and hauled overland by wagon. It may not have been of the same weight. Her after slanted shield was covered over with boiler iron - reportedly only 1/2 inch. Loose rails were later laid over the fore and after decks at Vicksburg. There are reports of a similar treatment for the casemate upper deck. Oddly this proved an advantage when they had to toss some of it overboard to lighten ship after she grounded on some tree stumps. In general, we can assume that Louisiana, Arkansas and Georgia had similar ironing techniques. The clinker is the fasteners. Firing tests in Virginia regarding different ironing schemes compared rail iron, laminated thin plate and heavier plate. Both the experimenters and the Tifts, who had a backup plan to use rail if plate was not available, agreed that the rail iron used for the tests was not adequately fastened. Louisiana's shield held up very well to essentially point blank firing from heavy Union sloops. Arkansas faced similar close-in fire above Vicksburg and her shield was heavily damaged. Some of it was probably the result of more cumulative hits because the action above Vicksburg came during daylight hours which improved targeting versus the night engagement at the forts below New Orleans. Although this type of T-rail ironing was claimed to be similar in resistance to laminated 4 inch ironing consisting of 2 layers of 2 inch plate, this conclusion is doubtful. Arkansas' vertical shields on the sides of the casemate lacked the additional advantages of sloping armor. In the case of the Georgia, we know that it was proposed to stabilize the reversed T-rail by pouring cement or metal filings into the gaps. Rebel and I both think this may apply to Louisiana and there are recovered portions of Georgia that seem to support this technique. I've never seen any documentation suggesting that it applied to Arkansas. The issue of when and how much pressed cotton was brought aboard and whether it was backed with a second wooden bulkhead behind the sides of the shield is another interesting topic.