The California Public Employees' Retirement System, the largest public pension fund in the United States, earned an estimated 19% return on its investments in 1997, surpassing the 12.9% it earned in 1996, CalPERS officials said. . . . Chicago-based AMF Bowling Inc. said it will acquire closely held Active West, the fifth-largest U.S. chain of bowling lanes and the operator of 15 centers in Southern California, for undisclosed terms.