By "308" I assume you mean .308 Winchester/7.62 NATO. Is this by any chance a Lee Collet Die? I'm not real familiar with the collet die, but they don't work like a regular sizing die. Most dies size the neck undersize, then the expander opens it back up. The collet die squeezes the neck around a mandrel; looking at the instructions on-line it looks like you need to adjust the die so it bottoms out solidly at the end of the stroke without camming over.
From the instructions:
"ADJUSTMENT FOR LEE PRESSES Screw the sizing die in until it contacts the shell holder, plus one turn more. Run a case into the die. You will feel the primer being extracted, then the lever will come to an abrupt stop. At this point, the lever must be pushed firmly (min. 25 lbs.) to close the collet and size the neck. Extra bullet grip can be obtained by screwing the die in an additional quarter-turn.
"Other brands of presses that toggle or snap over center at the end of the stroke provide no feel and can damage the collet neck sizing die if adjusted as above. We suggest the die be screwed in until the die contacts the shell holder, plus 2 FULL TURNS This will prevent the press from toggling over center and give the operator feel of the collet closing."
Some folks swear by the Lee Collet die. I see no advantage to it. I've switched to the RCBS X-die for my M14; it's supposed to give much longer brass life than standard full-length sizing dies.
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