I had a partial case head separation using a 1.8oz buffer

[LRRPF52]

I am keeping headspace on the table, but since I don't need the science from it to explain my failure model(s) and since I don't think it is dimensionally significant as compared to the feed cone depth issue, I have it very low on my list as a significant contributor to this.

Again, we have mostly commonality and agreement here in theory! Just not significance.

The only part I disagree with 100% is that you will never rupture a case in any scenario in battery where the pressure was lower than an earlier pressure. This is what I was getting at with LRRPF52 earlier. Again, prior to the rupture, pressure was rising and rising, never falling. Then right at the rupture it is at peak value. Right after the rupture, the pressure will immediately start dropping. So there will never be "post-peak/dwell-time" phase pressure to rupture a case in-battery. If it didn't happen at peak pressure, it's not going to happen at any lower pressure after that.

This last paragraph supports the partial extraction model, no others. Pmax happens right after ignition. 47,000-52,000psi venting through that failure point on the brass would not leave brass looking that clean. Notice the lack of eschar/sootiness.

If you’re not convinced after seeing that he used a 1.8oz buffer, I would suggest spending considerable time studying the AR-15 operating system some more.

Carbine buffers: 2.9-3.0oz
H1 buffer: 3.7-3.8oz
H2 buffer: 4.6-4.7oz
H3 buffer: 5.0-5.4oz

I don’t think I’ve heard of a 1.8oz buffer before in the past 35 years of being eyeball-deep in AR-15s.

There’s our culprit. 123gr 6.5 Grendel, especially with AA2520 or any of the other ball powders like BL-©2, CFE223, H335, etc. would have done the same thing with a 1.8oz buffer on the back end of the BCG.

I started out using a Spikes ST-T2 (4oz)in my first 16” Grendel build if I recall.

Guys, my main reason for posting here is to help out other people to get set up, and to troubleshoot any problems they might be having.

It isn’t to argue ad nauseam about distractions from the roots causes of the problems.

Had I seen this earlier, it would have jumped out at me like a lightning bolt.