Would suggest you take a look at something that gives you a numerical value as to just what size your cases are after firing. In short, use of calipers to provide length of case from base to shoulder area, datum line on shoulder. I use a Moe's gauge or the Sinclair kit which does the same thing(RCBS offers similar tool.) Measure new unfired case vs fired case in your gun and you gain a picture of the amount of growth of the case upon firing. Then you can set your full length die to bump shoulder back to something less than reading from fired case to insure chambering. Compared to a bolt gun, the M1A's/M14's are "case eaters" for there is a whole lot of action taking place upon firing. Round is jammed into receiver, fired, yanked back out and that brass sees a lot of violent action. Reason for most not using brass more than a few times, say three or four at most to avoid case separation. The gun does not know that a partial case is in the chamber and it's going to send another one right behind it. As well put in above post, you do not want any grease/oil on brass or chamber for that can lead to big pressure spikes and problems. Just a suggestion.