RCBS X-dies, primer pocket uniforming
I'm on my 7th reload of LC 93 and 68 brass. This stuff is exclusively loaded with and a fairly stout load that throws a 178 AMAX at 2625fps from my M1A (with an Accuracy Speaks vented gas cylinder plug to bleed off the excess port gases and eliminate bending the op rod).
I haven't had a head separate yet. I think the secret is the RCBS X-die I use to resize the brass. First, I trim all my cases according to RCBS directions which specify .005" under minimum trim-to-length, which makes it 1.995" as the starting case length. After 5 firings, the cases stopped shrinking at ~2.007-2.008". I check the inside of each case before reloading for indications of head separation, but so far, it hasn't surfaced. My cases used to show separation tendencies between the 2nd - 4th firings with regular sizing dies. I set the X-die to bump the cases by .003" also. Make sure to deactivate the gas plug in order to maintain a true case headspace sample. You don't want the ejection process to stretch your cases and distort the headspace measurement.
To alleviate the possibility of doubling or slamfiring, I use a primer pocket uniformer instead of the pocket cleaning brush, and ream the pockets square and ~.007" deep. As I recall, Zediker suggests .004-.011" as an acceptable depth. I haven't ever had a double since I've begun the uniforming regimen (~2000 rounds).