Well I just assembled the gun and with a chambered FLS Lapua case it takes substantial effort to drag a .002 feeler out of the action. I estimate clearance at .0015. When I first set up the gun this is the way a .001 feeler would pull out with similar effort. So I gained a single thousandth but this could be just wear and tear or just what didn't spring back from a load that seems to be too hot. I remeasured with a sized bulletless case and the measurement was the same. Bottom line here is it was NOT headspace so that only leaves pressure, despite primer and extraction indications to the contrary. Of course, another poster mentioned defective Lapua cases and I can't rule out but some sort of pressure spike seem more likely. I've always had good luck with aggressive starting loads and am not the most conservative handloader but am meticulous about assembling rounds and gun setup. Everybody I know backs off starting loads further from max than I do and I guess my luck ran out. Mag primer, bullet seated to rifling, possibly a case with thicker walls (less capacity), and a springy action (compared to a bolt) formed the perfect storm. Why does everything happen together??? I'm still working on my house, I'm helping both my sons work on their houses, fishing is red hot, and now this! Good thing I'm retired or I'd need a rubber room. I'll be pulling the slugs and starting over. Thanks for the help, all.
__________________
ED PANZELLA
"SAVE A COW, EAT A DEER"