You do eactly the same thing for rifle cases loading lead bullets as you do pistol cases loading lead bullets. You bell mouth them.
Lyman makes an "M" epander die that both slightly flares and enlarges a short part of the case neck to accept the cast bullet base. It accepts the bullet base perfectly, and helps to keep it aligned as you seat the bullet.
You can do the same thing with a hand-made tool. Use a file to shape a 5/16" brass or steel rod spun on an electric drill motor or drill press. A lathe is easier, of course. Make the flaring end a stepped affair with .312" diameter stepped to .308" diameter. Attach a wooden dowel handle, and use it to press into the mouth of sized and primed cases. Lead shaving goes away!
John