Your .30-06 ammunition with /B/N/4/40 headstamp was made at St. Louis Ordnance Plant in 1953, in lot numbers one through four (an unfinished case exists with “5” also, but no loaded ammunition has been observed with that lot number). It was a contract for the U.S. Government, for ammunition for use in whatever convert operations they chose to use it in. It was not made specifically for the “Bay of Pigs” fiasco.
Similar rounds were made by Twin Cities (AN) and Lake City (CN).
These rounds are, like all ammunition, collectible, but are not rare. I have a full bandoleet of the St. Louis ammunition, lot 2, that I simply have not gotten around to firing yet. It is packed in a standard olive-drab 6six-pocket U.S. bandoleer, each pocket holding two, five-shot Springfield-type steel clips, with end tabs, nestled in a carboard pocket within the pocket of the bandoleer intself. Standard U.S. packaging, although the use of Springfield clips in a 1953 contract is interesting of itself, and I have no information as to why that particular arrangement was done.
The bandoleer has no markings other than a stampled representation of the cartridge’s headstamp on it.
The ammunition is Ball M2 Alternate, which differs from Ball M2 in having a GMCS bullet jacket, rather than a GM jacket. Bullet weight is 150 grains. The primer is non-corrosive.
Hope this helps.
Reference: “.30-06”, by Chris Punnett, page 312. (This is one of the “must have books” for anyone interested in U.S. military ammunition).