John, My apologies, I misunderstood, I'm on travel and I realized what you where saying after I posted but I had already boarded a plane. My statement on the guns being ordered from Fort Pemberton was general, the details being sketchy. Parts of Moores' command and two big guns from Mobile where turned away from reenforcing Fort Pemberton by that commander when it was obvious that no more attacks were coming his way in early April. Some of these units being in Yazoo City at the time. So we have a succession of movement of guns between Fort Pemberton, Yazoo City and Snyder's Bluff in this short period. It is obvious that the need for anti-shipping type guns at Snyder's Bluff was intended when Pemberton ordered the guns moved from Fort Pemberton by the words he used in the messages. He did intend that a force stay to guard the Fort, around two to three hundred men but no detail of what, if any, guns where to stay, (I may have miss it). But the situation was very fluid and guns were being moved in all directions. One section of the Pointe Coupee Artillery moved from Fort Pemberton, to Jackson to board a train to Morton, then moved to Edwards Station, and got caught up in the Battle of Baker's Creek, all in a span of two to three days -they mentioned their guns, all regular field pieces, no Whitworths.
Until I see a document of a third Whitworth within Mississippi in those months around the seige of Vicksburg, I'm going to have to go with the number of Whitworths as two. If it appears sometime in the future I'll gladly correct myself.