David - You make one leap of faith: the Whitworth at Ft. Pemberton "was removed to Snyder's Bluff," as opposed to these being 2 different Whitworths (and in addition to the one kept at Vicksburg). My "worry" is Gen. Sam. Cooper's report, 3 January '63, to Beauregard regarding the five Whitworths landed at Wilmington NC, from the GIRAFFE in last days of Dec. 1862: "The guns have already been disposed of by the Secretary of War -- one retained at Wilmington, one sent to Charleston, one [sent] to Mobile, and one [sent] to Vicksburg. The fifth belongs to the Navy Department." (OR, ser. 1, v.18, p. 817). Charleston, Mobile, and Wilmington each got the assigned Whitworth, are we to believe Vicksburg didn't get its third gun? If it didn't go to Vicksburg, what happened to it? It could be at Augusta, GA, as late as February '63 (OR, s.1, v.14, p.866, 876), but still time to get to Vicksburg. That all said, there seems no hard evidence of a third Whitworth in Mississippi.