I would resize the brass in what ever Lee Loader you have, then try the empty hulls in your gun. Most 7.62x54 russian rifles I've seen are bolt actions. They are more tolerant of "slightly" larger shells.
If this works fine, then consider only loading your reloads to starting or no more than mid range of the power you are going to use. The lower pressure rounds will expand the cases less and allow them to 1)last longer, 2) go longer before any full length resizing is necessary.
If you have the Lee loader that uses a Hammer as part of the loading process, consider keeping that and getting a cheap Lee press to handle the heavy work.