Jack,
You have the 5.1 type I and type II shells at rarity 8 in your book but I haven't seen a 5.1 on dealer or auction websites anywhere for some time now. In fact, if you check Harry Ridgeway's reference archive or Jack Milton's page you don't see a 5.1 or a 6 anywhere. I've seen lots of 15" Dahlgrens (rarity 9s in both single and multi-fuse) and James Bolts (rarity 9s) in the last few years in abundance. Are they, in fact, more rarer than you have them listed as? I, too, would love to add a Hotchkiss over 4" to my collection.
Garret