Can anyone help?. Does factory loaded ammunition have a shelf life, I assume not as there is nothing marked on the box?. Can the charge lose its potency over time?. I ask this as I have been offered a 100 rounds of 300 winmag (200g load, federal express, in the old style packaging), £15 for twenty. Seems like a bargain, but i do worry that it may be inconsistent and give me problems with accuracy etc. Am quite new to the sport, so any advice would be appreciated...