David -
In 1861-2 the Armstrong gun was absolutely unavailable to Americans; both Woolwich Arsenal and Armstrong's Elswick co. were devoting all energies to the British army & navy. There is a lot of potential for almost random misidentification of (especially?) English artillery, especially descriptions of guns not actually seen (esp. by newspaper men).

The "Richmond Dispatch" of Feb.2, 1861, that you found is especially fascinating. The "Armstrong gun" arrived in Charleston, headed to Georgetown SC and a "Mr. Weston." This is all "pre-war"! Mr. Weston is certainly Plowden C. J. Weston of the Georgetown area. I found another reference that Weston was dickering for, or had obtained, a Whitworth.

The most famous misidentification of one of the guns from the Bermuda, is that the "Lady Polk" of Belmont TN was a Whitworth that arrived on the Bermuda. "Lady Polk" was a rifled columbiad made at Tredegar. About a dozen (maybe more) Blakelys were aboard the Bermuda, field-gun sizes, mainly 12-pounders.

John