Bruce,
None of the present commercial .416 Rigby Federal or Norma brass I've used is "lighter" than, say, .416 Weatherby brass. The case capacity is just slightly less than the .416 Weatherby, and loading the Rigby up to near Weatherby velocities didn't make extraction sticky, expand primers pockets, or cause any other problems except, of course, more recoil. I didn't find it too bad, but all the three buffalo I've taken with my CZ were taken with standard velocity loads, and they worked just fine--as they should.
