Headspace is tight, I believe(checking with a straightedge), and under the 75 gr load of 4064, there is no stretch. These are 2.6" Starline cases. Cases started seperating after 4 reloads, with the telltale crack starting 3/8" in front of the rim, when I was using something like 61 gr of 3031. Should I be using a dacron filler, if the case is 90% full, like with the 4064?? How would H4350 work out--would probably be a full case? PS: The bottom screw is not engaged, the top screw bears about .008" against the barrel, to lower the left barrel. Both barrels print at the same elev, but 4" apart at 50 yds(not crossing).