8-0-8 is a designation of weight in hundredweights, quarters and pounds. Each hundredweight weighs 112 pounds; or 896 plus 8 pounds equals 904 pounds.
The hundredweight was part of a system of measures of weight that was in commercial use throughout the British Empire from ancient times (as legally defined in 1340 by King Edward III, the hundredweight was equal to eight stones of 14 pounds each)--- into the 1970s.
Does the piece weigh that much?
The crown and P go together to assure the purchaser that the gun had been proved (tested to a standard).
Don in SoCal