I'll have another stab at this - Its too much fun!

.22 LR
6.5x47 Lapua - Borden or BAT action
.303 British - Hagn falling block with take-down barrel (maybe Epps or Ackley improved chamber)
9.3x74R - Westley Richards detachable lock DR
.500/.450 - Holland and Holland Royal
.375 H&H - back up rifle with Mauser action and take-down barrel

D'oh! - that makes 6 - I'm not very good at this!