The condition you are looking for is called incipient case head seperation.
The best check is to straighten a paperclip and bend about a 3mm long section 90 degrees to the tip and run it inside the case feeling for the ring.
And I would bet that was SAW brass.
If you have a collapsing stock, you collapse it all the way. You hold the rifle straight up and down in your support hand, with your strong hand on the charging handle. You bring the rifle straight down to the ground on the buttstock simultaneously pulling the charging handle.
This is your best bet to clear a stuck case that the extractor is sill holding onto. Works a fair amount of the time.
Always always always collapse your stock in all the way before mortaring. Then you want a nice square strike to the deck.
Sounds easy, but it’s just as easy to fuck up.
From another thread:
Originally Posted by dbrowne1
Used to clear a stuck round or casing. You kneel down and hold the rifle vertically with the stock toward the ground, holding the foreend with your left hand. Close the bolt over the stuck case/round and then slam, or “mortar” the rifle onto the ground while holding open the release latch on the charging handle. It generates a sudden “jerk” on the bolt that can help pull the stuck case/cartridge out.
Originally Posted by Gutshot John
Make sure you collapse your stock all the way first.
Originally Posted by Luke_Y
Also, take care to strike the stock squarely. There is a tendency to strike on the toe resulting in breaking off the toe on standard m4 stocks.
And, be very muzzle aware…
ETA Oops, I could have clicked through to pg2 to see that it was already answered- instead of the cut and paste. 
Glad to see the extractor worked so well. I keep one in the 3 round core of my MIAD grip, along with a derlin pin punch and a A2 front site tool.
The problem could have also been a weak extractor spring. In each of the weapons that I examined there was another common theme- LACK OF LUBRICATION. Someone has convinced some of these guys that lube is bad in the desert because of the dust.
For anyone looking for the broken shell extractor, here is the website. They are only $10.
http://www.cjweapons.com/aspcart45/default.asp?page=307&start=1
“if you don’t scrub the chamber with solvent and a brush every 200 rounds then you will get torn cases and broken extractors.”
Its a joke from this thread
https://www.m4carbine.net/showthread.php?t=49796
Sounds like a bigger issue for that many shooters to be needing to mortar rounds out. 
hahahahahhahahaha