When I lived in Nevada years back, we would organize "Big Bore Bunny Busts", with nothing under .375 caliber allowed. There were an awful lot of old BP cartridge rifles, single shots, levers, side by sides, and bolt actions, in a dizzying array of calibers from 38-55 Winchesters to Paradox guns to old European military BP rounds, up to and including 450 NE. I used to participate with a 375 H&H Mark X Mauser. What happens to a jackrabbit when it gets hit by a 250 gr bullet is not easy to put into words.
I have shot everything from chucks with a 22 LR, to tiny ground squirrels with a 45-caliber rifle. My favorite is still my 22-250, which will turn a large squirrel into mist in an instant. I have sat in one spot for up to 8 hours, shooting as much as I could endure for days at a time, then spent evenings reloading so I could do it again the next day. Start out with 1,500 rounds, shoot 300 rounds a day, and reload as many as possible before exhaustion sets in. Next day, get up before light and do it all over again. Sometime around day 7 or 8 you run out of ammo, pack up and go home.