I am of the 'headspace on shoulder' and 'rollcrimp' factions.
Some time ago I trimmed back the casemouth on a sized 357sig case, and it seemed to change the seating depth not at all.
I ran another empty, sized case through the RCBS seat+crimp die, and it came out with a definite roll at the casemouth.
Try some canelured hardcast from Hunters Supply. Consider getting an aftermarket land+groove barrel if you shoot Glock.
http://www.hunters-supply.com/shop/p...roducts_id=154
-shu