If you are lucky, the once-fired brass was fired in a rifle (or rifles) whose particular chamber dimensions are smaller than yours.
Chamber-test each fired round to see if they chamber. If they do, then you are OK. If they don't, then you still don't know. Separate the two groups.
But your rifle is likely to be semi-auto? Neck-sizing (Lee tool or in a press) only is not for rifles with action types that do not provide a lot of leverage (semi-autos mostly) when chambering a round.
A cartridge that doesn't allow locking of the breech gives you a jammed gun at best. A partially locked breech can come open on you with potentially catastrophic results.
You can be safe with loaded ammunition by chamber-testing each loaded round before attempting to fire them.
Generally, neck-sizing (with the Lee Tool or a press) is not used with semi-auto guns for that reason.
Last edited by Lost Sheep; September 1, 2012 at 07:49 PM.