They were just as accurate as pretty much any modern gun. While there are modern manufacturing techniques and new bullet designs to eke out as much accuracy as possible for mile-long shots, your average 2019 hunting rifle isn't going to be so much more accurate than a World War II service rifle as to make a difference in the hands of an average shooter. Rifles capable of hitting man-sized targets at 300+ yards have been made since at least the 18th century.