Eicher, p. 660; Alexander, p. 497. William N. Pendleton's report after the campaign in the Official Records, Series I, Volume 36, Part 1, pp. 1036–40, accounts for only 213 guns.
nps.gov
cr.nps.gov
NPS. There was no significant fighting on May 7 and some authors, such as Welcher, p. 941, use the dates May 5–6.