303s are notorius for case base swell. If you don't full length resize you may never get them back in. If it's a new chamber cut with a good reamer it may work with neck only. I wouldn't use Lee products unless there was nothing else. If you're buying, get RCBS and there will be no problems. If you bend a decapping pin with Lee for instance, you need a whole new assembly. With RCBS, you change the pin. If you're going to reload you will need to trim all the time. You can't get into this ankle deep. It's all or nothing. Get hold of someone that's done a great deal of loading and get lessons. Buy the manuals and read them. About three would do. Then your ready to start asking questions. Otherwise you have no basis to start from. This area should not be entered blind.