another etymological urban legend?

[Arnold Zwicky]

on "son of a gun": there are two really obvious (and not incompatible)
sources, both involving metonymy - "gun" the weapon extended to
the wielder of the weapon, that is, a soldier; and the metaphorical
"gun" 'penis' extended to *its* wielder, a virile man.  the first
would be only mildly pejorative, the second not at all.

in current usage, "son of a gun" is exclamatory and scarcely
pejorative, if at all.  its use in exclamations like "well, i'll
be a son of a gun!" (or just plain "son of a gun!" 'wow!') and
in affectionate address forms like "how are you, you ol' son of a
gun?" make it very different from "son of a bitch".  "he's a
real son of a gun" is just perplexing to me, certainly not an
insulting reference (the way "he's a real son of a bitch" is).

what's the history of its uses?  can we tell from the context
of the earlier citations?

the boy-born-on-ship story sounds quite far-fetched to me, and
i'm not even sure about the euphemism account ("gun" is good as
a rhyme for "son", but an extremely poor substitute for "bitch",
to which it bears no phonological *or* semantic relationship).
maybe the history is pretty prosaic.

[by the way, aren't there insulting/pejorative occurrences of
"son of a dog" from the 19th century or earlier?  or is this
just bad-movie dialogue?]

arnold (zwicky at csli.stanford.edu)