I haven't killed any elephant with the 7x57 (or anything with solids), but have used it on springbok and pronghorn out to around 375 yards and it worked fine. Have also used it on bigger game including impala, warthog, bighorn sheep, mule deer, wildebeest, elk, kudu and moose out to 250 yards, and have yet to experience any problem--other than a couple caused by operator error.
Bullets used have included everything from cup-and-cores to Nosler Partitions to bonded cores to TSX's. All the animals died within at most 100 yards of being hit, and 90% went 50 yards or less.
