I found out from a Dixie Gun Works gunsmith that you're exactly right. What goofed me up was their description of their basic case:
"For the nitro express shells; drawn case, measures 3 ¼” long. Use 210 large rifle primers. We recommend black powder only. Will make the following cases: .577-450 Martini Henry, .577 Nitro Express, 2 ¾” and 3” long, and .577 Bottleneck Snyder. Box of 20."