I had previously put in feed ramps that stupidly cut into the base area of the chamber in the barrel. Learned my mistake when I test-fired the rifle and blew a magazine bottom out when a case failed.
I welded up the feed ramps in the receiver and hand-filed them to match as well as I could the factory shape. Had to put a new barrel in and re-headspace the rifle by welding up and grinding the bolt locking wedge.
This rifle has always been touchy about magazines - some feed well, others miss feeding occasionally. Today, I had a misfeed, and removed the magazine. Loaded the misfed round by hand and fired it downrange.
Felt sharp pains in my left arm and right fingers, and a blow to my chest at the base of my breastbone. Thought I had been shot! Numerous small cuts in my left arm, some small punctures in my right fingers, and a weeping wound in my chest - though no hole in my shirt.
Found the case had ruptured about 1/4" above the base. Here's the part I found jammed in the breech:
The remainder of the case still in the chamber:
As far as I can tell, when I chambered the round, the bolt failed to go completely into battery, and the hammer fell on a partially seated case. The broken-off part of the base shows an extruded area, like the case attempted to expand into the now-too-large headspace gap.
The welt on my chest - likely a large chunk of brass:
Welts on my left arm:
My camera's flash obscured the marks on my right fingers. Those and the left arm probably got peppered with small metal shards. Nothing actually got stuck under my skin, luckily.
Moral of the story - always wear those safety glasses, and don't fire an FAL without the magazine - and make damned sure the dang bolt is in battery!