Speaking for myself, I don't have a tremendous amount of what I would consider "old" rounds, I believe most of my stash had been manufactured / loaded within the last 6 - 10 years (and I rotate my stock by date - OCD is a terrible disease) BUT - I do have some which is at least 20 years old, and some .22LR which may be at least 25-30 years old. Doing the search in the forums, I discovered a thread addressing the viability of primers over the years - the general conclusion of the Air Force was 20 years before dudding (if kept in a temperature - controlled space). I have loaded and shot powder that is over 25 years old, so there is that as well. We all know storage is key....no extremes of heat or humidity can be good for the little buggers in any caliber, container, or package. And, inspection of the rounds is a given (even if it only happens occasionally) for telltale signs of corrosion or discoloration. So, given the assumption of correct storage and inspection without subtle signs of deterioration - how long do you let it go before recycling? And, would your answer change if you had acquired the rounds without knowing their entire history?