Since they are being reloaded it would be more related to how much they are being resized, so could be FLS die and how you've adjusted it.
I never did a full FLS for my M14, my cases were a snug fit but also reliable feeders - the FLS die wasn't screwed into the press for max FLS if you know what I mean. I check case length and adjust to max after each firing so don't really know the figure for how much they stretch. I use my caliper as a go-no go length measurement.
I'm using full length die just barely contacting shoulder.
