The very first Confederate rifle-shell I dug was a 2.9" Brooke, back in 1975, I think. It was an "overshot" dud, fired from the main CS trench-line on the Dallas Road toward the Bald Knob. I still own it, of course.
Steve Griffith was hunting with me that day. When I pulled it out of the ground, I yelled to him "It's a Brooke!!!" The result of my scream was that he found a 2.9" Read-Blakely as he walked toward me to see my Brooke. I suspect he also might remember that day.
I wish you good fortune when you go digging in that area.
Regards,
Pete