Hommer,
I agree with you on at least 100 rounds.
I believe I can get a rough idea of the rifles potential within the first 25-50 rounds, but you are correct with the 100 round figure.
My 338-06 with a stainless fluted Lilja barrel was a dog until I put about 120 rounds through it, now it'll put 5 215 grain Sierra's in around 5/8 - 1".
I did the barrel run in thing as I do with every new rifle or barrel I have, I hate doing it, takes up far too much shooting time, but I'm just not game enough not to do it, good barrels cost money.
I'm sure the 416 will shoot well enough for me to hit things with it in any case.

David.