Thank you. I'm checking out the Whitworth angle. I have located three areas where Whitworths were mentioned being used. All were in fixed positions. Two are mentioned at Vicksburg in November of 1862; On April 7, 1863 one is mentioned at Fort Pemberton being manned by a detachment from the Point Coupee (Louisiana) Battery, it is described as a 3 inch (eighteen pounder bolt) on field carriage;
another is mentioned at Vicksburg on April 18, 1863; Brigadier-General Hebertís brigade is mentioned to have one Whitworth positioned on the Jackson Road in the trenches at Vicksburg on May 17th, 1863, it had been used at Snyder's Mill before that. In the reports of guns captured at Vicksburg, one is a Whitworth.
Since these guns were rare, and very sought after, they seem to be given special attention in the O.R. by the Confederates. It sounds there was at lest one, most likely two Whitworths in the Vicksburg area but I believe they would not have been assigned to support Infantry. Their primary missions were anti-shipping and counter battery fire.