from The Century Dictionary and Cyclopedia
- n. A pistol. Marryat.
- n. An instrument for removing the bark of oak and other trees, for use in tanning.
Sorry, no etymologies found.
Pulled out his barking-iron to send daylight through his brain; 
"Now, my feller prig, honor's what I expect from you, and, to remind you of it, Levin, I'm a-goin 'to pint this barking-iron at your mummer, so that if you patter a cackle, a blue plum will go right down your throat."
Here, "said he, dealing Rust a heavy thump upon the shoulder with the butt-end of the piece," take back your snapper, and look you prick the touchhole, or your barking-iron will never bite for you.