Well, I just received 2 boxes of ammo for my .300WSM, one is Federal Premium 180 Nosler Partitions, and the other is 180 Barnes TSX. I thought I had ordered the Accubonds, but realized that I actually ordered the Partitions - not a big deal.
Anyway, as Headache suggested, I did in fact place one cartridge in the chamber and the rattling did in fact go away about 75% or so. When I put a round in the magazine only, the rattling did in fact go away about 90% When there was both a round in the chamber and one in the magazine, it was 100%.
I should note that I was really shaking the rifle pretty good to try and see if it would make any rattling noise. So although I could hear some rattling at the 75% mark, I seriously doubt that I would shake that rifle up that much in the field. Also, even at 75% it may be a little tick here or a little tat there - nothing too bad.
So I guess that when I go hunting in the field, whether on my way to a box blind, or just hunting while walking, I should have at least one cartridge in the magazine to make sure that the bolt won't rattle and make any noise.
Zachary