Bill:
In my mind, a cannon has no rifling in the barrel. They were basically smooth-bores, I thought. I looked up cannon in the OED and found this: . A piece of ordnance; a gun or fire-arm of a size which requires it to be mounted for firing. (The leading current sense.) The following varieties are mentioned in the 16th-17th c.: Canon Royall, height 8 1/2 in.; shot 66 lbs. Canon, height 8 in.; shot 60 lbs. Canon Sarpentine, height 7 1/2 in.; shot 53 lbs. Bastard Canon, height 7 in.; shot 41 lbs. Demy Canon, height 6 1/2 in.; shot 30 lbs. Canon Petro, height 6 in.; shot 24 lbs.
The various sizes are of interest, particularly the canon petro. I wondered if it has any relationship to a petard, but apparently it doesn't. There's no definition in the OED for petro other than as a combining name for rock or petroleum, but petard comes back as having derived from the french word for fart, peter, with one of those accenty things over the first e.
I also looked up rifle; the first use of that word with relation to a gunbarrel is 1750, the middle of the 18th century, which lends some confirmation to my supposition that cannon is an earlier invention and was essentialy a smooth-bore.
TEd
