Being interested about the trace of chamber pressure, I found this website that seems to suggest that during a normal firing cycle there is only one peak on the trace.This can be explained by considering the pressure cycle. There's two main ones for a "normal" discharge. The first is detonation and partial burn causing obituration of the case, sealing the gas pressure and driving the bullet into the leade, then the second is the build up of pressure as the powder ignites fully, needed to swage the bullet and drive it down the barrel. If there's sufficient gas leakage on the first pressure cycle or only a partial ignition of the powder, it may well drive the bullet and just jam it into the rifling (partial swaging) then it can lead to dangerous pressure build up within the chamber upon complete ignition of the powder charge, which is why under loading can be as dangerous as over loading (partial swaging) creating a massive pressure rise.
All of this makes me glad I got shot of my HMR which was an accident waiting to happen. I lost count of the squib rounds encountered, on the face of it from ammo I'd checked as some of the hairline cracks in the case are hard to spot.
The issue hasn't been resolved at all. It stems from the need to prime the rim before necking the case down so the brass often work hardens and cracks. Many may have been lucky and not experienced any issues with their HMRs but a huge number of users have and how this can be acceptable for commercial ammunition is beyond me.
There are examples of double peak traces, where the second peak is reached as the bullet exits the barrel.
Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace
Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.
www.shootingsoftware.com
