BC shooter,
Win 300 mag is a very strong casing, it shouldn't really matter to much as to the brand. I do belive tho that the Federal might be the heaviest casing, at least this has been my experience with the 300 and 7mm. But then you might not get as high of velocity with the heavier case than you could with the lightier one, being, pressure will climb quickier with a given load. Just like milatary brass is heavier. Trial & Error.