What is the battery of nine?

From a PDF Ahmed sent to me:
5.6x52R Double
.300 H&H Flanged Double
.303 British Double
.375 H&H Flanged Double
.500 Nitro Express Double
.600 Nitro Express Double
10-Bore Shot & Slug - Side by Side Rifled Choke
10-Bore Shotgun Side by Side
28 Gauge Side by Side shotgun