While the standard projectile idea is a good one it ain't gonna happen, the government simply will not go to those efforts for us. Remember, they're trying to get rid of us.
Realistically, the best we can hope for is that they publish a standard list of pellets to be used in testing by all forces. And that if a pellet on the list becomes unavailable they publish an updated list showing what will be used instead.
British Standard Balls? Load of balls more like!