Odd ammo incident question

[MH64]

Was out shooting the other day with a few of my AR's.
Had a round that I thought went click but noticed a bit of smoke coming from the ejection port side. Checked rifle by dropping the mag first, still had ammo in it, and then retracting the charging handle. A round was ejected, bullet still attached but alot of black soot on the case covering the entire rear portion. Couldn't tell the condition of the primer.
Unfortunately the round rolled over and off the side of a drop off and couldn't be retrieved for better examination.

Now I broke down the rifle and made sure there wasn't any bore obstructions and everything seem just fine.

Any ideas what this could have been?

Haven't had anything like this happen before with any ammo.

Ammo was factory UMC green/white box 55gr fmj.

[Heavy Metal]

No flash hole in case.

[-gary]

Had the same thing happen to me on a Wolf round. Here's what was left of the primer.

http://www.garydickerson.com/photos/275480615_BRUbq-L.jpg

[MH64]

Did the round fire or was the bullet still in the case?

[-gary]

Still seated, exactly like you described. You can see bits of slag whee the primer melted away as it fizzled.

[markm]

Interesting. As a reloader with a Dillon, I have this primer mashing happen from time to time.

It's quite obvious when the primer mashes sideways..... so I've never had one make it into my weapon.