Puncheon
Punch´eon
n. 1.
1. A figured stamp, die, or punch, used by goldsmiths, cutlers, etc.
2. (Carp.) A short, upright piece of timber in framing; a short post; an intermediate stud.
3. A split log or heavy slab with the face smoothed; as, a floor made of puncheons.
4. A cask containing, sometimes 84, sometimes 120, gallons.

So, a rum puncheon would be difficult to chug-a-lug.

Edit:
"Now, you could work that into conversation if you wanted to force the issue. `Sir, do not dare you clepe me in such a fashion or I shall be compelled to thrash you with a puncheon or clevis, whichever being the most geographically convenient!'" Mike Kelley, Writer: If You Don't Know What Clevis Means, The Austin American Statesman, Apr 22, 1991

Definitions 2 and 3 seem to fit the context of the quote.

Clevis
(n.) A piece of metal bent in the form of an oxbow, with the two ends perforated to receive a pin, used on the end of the tongue of a plow, wagen, etc., to attach it to a draft chain, whiffletree, etc.; -- called also clavel, clevy.