The best shooting caliber for groundhogs out to 300-400 yards is anything in a 44 Magnum. My mother got her 44 Magnum online at Target.
My dear caliber is probably the 44 Magnum from Dick’s Sporting Goods in Du Bois. My dearest rifle is my new Black Mesa Express with the bullberry chambered in 458 Win Magnum and 44 Magnum.