The Ordnance BL 12 pounder 6 cwt was a lighter version of the British 12 pounder 7 cwt gun, used by the Royal Horse Artillery. The "6 cwt" referred to the weight of the gun and barrel to differentiate it from other 12 pounders guns. One hundredweight (cwt) is 112 pounds (51 kg), so the total weight was 672 pounds (305 kg).
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