this is absolutely serious....now listen to me......Is 800-X listed in any book for the (was it .303) ???...if not pull the bullets and don' t ever shoot them.

It' s possible but I' d be very suprised that 800-X is a powder for the .303

Only load charges listed in a reloading book printed by a recognised company such as Hodgdon, Hornady, Nosler, Lyman, etc.....