Ka-boooom and stumped

[alpine44]

The most important thing to keep in mind is that the bolt was closed after the event.

The BC was pushed back to the point where the cam pin would start rotating the bolt, but the bolt could not rotate because of the brass wedged between barrel and bolt. The bulge (belt) on the case will fit between the barrel and the bolt due to the chamfer radius at the breach end of the barrel.

Also, an out of battery discharge will not force brass into the ejector hole the way this event did.

All signs point to the fact that the powder charge developed A WHOLE LOT more pressure than desired. The question is: Why?

I agree with the assumptions that the powder measure is a suspect. It could have trown less powder (some got stuck in the funnel) or more (powder that got stuck on the previous shell came loose).

My gut feeling is that filling the case until the long tracer bullet bottoms out would not yield these drastic results. I may verify this in 2 weeks with the tree and string method.

I lean towards explaining the dramatic results with a low charge and a subsequent detonation or Secondary Explosion Effect. An indication of a SSE may be the smoking of the front to the cartridge seen in pic#4. A simply overcharged cartridge would have sealed well at the neck and would not show any smoking.

The outside temp was 54 degrees F and the cartridge was probably around 60 deg F.