Originally Posted by bigedp51
The chamber pressure of the .223 and the 5.56 are both 52,000 cup or 55,000 psi. The actual difference between the two is the throat and the shorter .223 throat will cause a pressure increase with military 5.56 ammunition.

[Linked Image]

The CCI 400 primers you are using have a cup thickness of .020. Just switch to a primer with a cup thickness of .025 and your primer problem will go away.

[Linked Image]

I would also advise using workup loads starting at the suggested start load and work up. This will teach you how to read your primers as the load increases.

Also your pierced primers are a sign you are bumping or pushing the shoulder back too far when sizing.

The primer after being hit by the firing pin will be pushed out of the primer pocket until it contacts the bolt face. This causes the primer to flow back over the firing pin and it can punch the center out of the primer.

[Linked Image]

[Linked Image]

[Linked Image]


My apologies, I stepped away from this project for a while and neglected to see that there was still ongoing discussion here.

I searched around a bit and came to the same conclusion that I should try a different cup thickness. One of the sources was the James Calhoon article that I believe is also the source of one of the charts you posted. http://www.jamescalhoon.com/primers_and_pressure.php

This past week I had a chance to make some new loads and to swipe by buddy's new magnetospeed chronograph. I used the same mid-range 556 load (according to Ramshot data) that was causing cratering, but I loaded them with CCI 41 primers. With the thicker cup I got zero cratering, primers that still had a radius on the edges, and groups under 3/4" at 100 yards. When I put the magnetospeed on the barrel I got readings of 3090, 3097, and 3095...which is exactly what I had expected (and hoped for) based on the pressure that should be there.

Thanks again for the advice. These loads will only be used for hunting. I wanted the extra velocity of 556 pressure to make sure that the Barnes TTSX opens up out to 300 yards. All of the plinking and practice will be done with my usual 223 reloads...which are mild and do just fine with CCI400s.