This topic is just too good to let it die! How about the prominent "L" seen stamped into a number of 3 inch Broun sabots. I photo'ed this example at Pete's during the 1980s. He had additional similarly marked shells. I strongly suspect it represented the maker Lenher & White whose invoices confirm the production of about 1,500 3 inch Rifle shells between January and May of 1864. This small Richmond foundry finished many of the six and 12 pounders cast by other foundries like Adolphus Rham whose invoices were frequently marked "unfinished" when the projectiles were turned over to the Richmond Arsenal. The Rich. Arsenal subcontracted the finishing to Lenher & White and supplied them with Bormann underplugs to fill the side-loading holes. When the Arsenal ran out of the obsolete underplugs, Lenher & WHITE began making their own small brass side plugs (with two spanner holes) like those dug around Petersburg and shown in Pete's book. So. add the "L" to your list.
Woodenhead