11 rounds in a single minute? That's amazing. The unit I'm looking at is Company D, 1st Illinois Light Artillery at the Battle of Raymond. The unit was facing the Confederates for at least an hour, maybe two. What does it tell you that they only fired 72 rounds between the four guns?

Here is the breakdown in number of federal artillery rounds fired during the Vicksburg Campaign:

Port Gibson: 3,900
Pursuit from Port Gibson: 82
Raymond: 620
Jackson: 476
Champion Hill: 3,422
Big Black River: 1,297
May 19 at Vicksburg: 9,598
May 22 at Vicksburg: 10,754
Remainder of the Siege: 111,614

If Company D fired 72 rounds, that leaves 620-72 = 548. DeGolyer's Battery (2 howitzers, 4 rifled 1841 six-pounders) was the only unit firing for most of the battle, and fought for about 3.5 hours. If DeGolyer averaged as little as 20 rounds per hour, then that's 6x20x3.5=420 rounds fired by that battery. Is that a good minimum number for 3.5 hours of combat?

That leaves 548-420 = 128 rounds maximum fired by the other artillery units at Raymond, which were 3rd Battery, Ohio Light Artillery (4 rifled 1841 six-pounders, 2 smoothbore six-pounders) and 11th Battery, Ohio Light Artillery(2 twelve-pounder howitzers, two smoothbore six-pounders, two rifled six-pounders). One of these units I believe was used to form a refused flank, and was almost completely unengaged for the duration of the battle. So that would leave the other unit performing the same role as Company D, 1st Illinois Light Artillery which fired a fairly lazy 72 rounds for the duration of the battle.

6x18=108
4x18=72
6x20x3.5=420
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estimated=600 rounds, actual = 620 rounds

Seriously wondering what the role of the federal artillery in this battle was. I'm beginning to suspect it was to stir up just enough smoke and noise to mask the troop movements of the federal infantry.