I shot old Remington and newer Winchester both 180 factory loads. I've got a boatload of 150 and 180 gr bullets I could load for the 303.
The Brits shot 174-grain bullets out of their Enfields so I wouldn't speculate on lighter weight slugs going in the direction you want. If I were reloading I would use heavier bullets and maybe even powders that come close to the burn rates of those that were used back in the period of the Great War. The rifle and sight is only half of the problem.
