While this is not a bench rest score it happened during the 18 Aug 2018 CBA Military match at the Van Dyne Sportsmen's club.
Jeff Heeler shot a 40 shot match offhand with his 71/84 Amberg .43 cal Mauser. Lyman 446110 at 350 grains, 24.0 grains of AA5744, WLR primer, velocity chrono at 1250 fps.
This is probably a 40 shot record and a 10 shot record for a Big Bore rifle.