A round with delayed ignition is called a "hangfire."
I saw one occur in an M16 about 1978, when I was in the Air Force.
We were qualifying on the range. At the end of the line of shooters, an Airman pulled the trigger on his M16 and it just clicked.
He probably thought it failed to feed, so he immediately pulled back the charging handle. The bolt was open when the cartridge went off, spewing hot brass fragments out the side of the M16 through the ejection port.
Luckily, he was the last Airman in line, and about 6 feet from a concrete wall. The rangemasters declared no more shooting until the investigation was completed.
But to their credit, they had us walk by single-file, carefully so as not to disturb the scene, and see the tiny flecks of brass that left their mark on that concrete wall, and the pieces of brass lying below it.
Then they got us together (about 20 shooters, as I recall) and reinforced exactly WHY you don't open ANY firearm if you experience a "dud."
You keep it pointed downrange and hold it there for 15 to 30 seconds (preferences vary).
Of course, in combat you take your chances but at the range -- wait!
I saw that brass-flecked wall more than 30 years ago -- and I wait 30 seconds before opening any firearm that experiences a dud.
AND I keep it well away from my face and body when doing so. Revolvers are particularly worrisome, because if the cartridge goes if, it can propel that empty case right into your chest or face.
I don't know how many times I've been at civilian ranges and see other shooters experience a dud, then immediately open the firearm to clear it. A brass .22 rimfire case is light and can likely achieve a decent velocity at close range, certainly enough to penetrate a T-shirt and layer of skin. I wouldn't be surprised to learn it can penetrate into the heart.
Now, this is a much longer response than you likely anticipated but I wrote it to drive home the point that a "dud" isn't a dud until about ..... ohhhhhh ... three centuries after the primer's been struck.
My understanding is that the struck primer, some believe, can be rendered even more sensitive if it's been hit by a firing pin and not ignited.
Good enough for me. I don't bring such cartridges home for souvenirs or disassembly to salvage components. I bury them, or throw them into a deep pool of water. I may be out the bullet, case and primer -- but not my eyes, a finger or life.
Yeah, I'm Mr. Cautious ... laugh at me if you must but I once saw a "dud" become a tiny grenade. Makes an impression upon a guy.
