The best brass I used for loading the 303 was stamped DZZ. Was a surplus brass and from the primers looked to have been fired from a machine gun.
with a bit of prep, this brass was awesome. Very tough and accurate. I used the Lee collet neck die to load and had excellent case life. Was able to almost duplicate 308 performance in my No4's.
Never tried IVI but would expect the same durability from them as well. I really like using surplus brass in my rifles. They stand up very well to the abuse I give them and are plenty accurate even for match rifles, after being sorted of course.
Jerry