It sounds like a headspace problem. If the chamber is worn, the headspace is too big and the brass expands too much and jams in the chamber. The only way to check it is to get headspace gauges and check the chamber on your rifle. You can rent them for about $10 including the shipping. http://www.reamerrentals.com/ProductDetails.asp?ProductCode=7%2E62x54R%2Eg
I use the second place most of the time.To repair the problem, the barrel needs to be removed, the shoulder and face set back and the chamber recut. Sometimes re-chroming the bolt face will make up the excess space instead of recutting the chamber.
I hope this helps you,