1st MS Light Artillery Co. G apparently served a Whitworth during the siege of Vicksburg...(it doesn't say but I'm assuming it is a breech loading 2.75 in. rifle)
There is also a marker for this on the Vicksburg Park...i believe the position for the gun was near the railroad cut...the marker states that the position is not on park property.
OR 24 Pt. 2 pg.381
Headquarters Moore's Brigade, Forney's Division
An 18-pounder, a 30-pounder Parrot; and a Whitworth gun were placed during the siege in rear of my line, and commanded by Captain J.J. Cowan.