In a paper in Journal of American Folk-Lore from 1915, entitled 'Songs and rhymes from the South', E. C. Perrow lists a song entitled 'Franky' (obviously a version of Franky and Johnny), which has been collected from 'Mississippi; Country whites' in 1909. Two stanzas in this song suggest the use of bull-dog as as a gun:

Franky went down to the bayou;
Franky heard a bull-dog bark;
Franky said "That's Albert
Hiding in the dark,
For he's my man; but he's done me wrong."

Franky went down a dark alley;
Heard a bull-dog bark:
And there lay her Albert,
Shot right through the heart.
"Oh, he's my man; but he's done me wrong.