The .455 Colt was also known as the .455 Eley , a different round than the .455 Webley. It was longer (1.388 OAL-.885 case length) , with a few grains heavier bullet.
I have a 1918 Colt New Service in .455 Eley.
Ya can shoot the shorter .455 Webley (1.227 OAL-.748 case length) with no problems other than a different point of impact.