Today I was at the range with my olyarms K23 stubby, while shooting, I heard a loud bang and my magazine was forcefully ejected from lower.

The action was jammed, so I separated upper from lower, further inspection revealed that the bolt carrier was broken at the bottom, the bolt hold the case that showed a cracked hole near the extractor, that was bent outward

I've examined the upper, and, the lug at 2'o clock seems to me slightly dinged on the inside (the part facing the chamber).

The bolt, apart from the broken extractor seem fine.

Now, my question is, what I must control? Locking lugs? chamber?

Is my 4-months ar15 ready for the trashcan???

Thanks anticipately for info, guys, right now, I'm REALLY upset, here in Italy is a real pain in the ass to obtain spare parts for ARs, and If I must install a new barrel, the cost and bureocratic bullshit here is such that I would prefer send my ar to destruction..(sigh..)

Was the case actually split?  It could be an extractor spring failure, is the extractor claw broken or just bent?  More info please.  

I cant really answer your question... But Oly arms is chambered for .223 only right? Would shooting 5.56 in an olyarms rifle cause that? Could that be what happened?

I doubt the rifle's ready for the crapper; not just yet. You'll obviously need a new bolt carrier and extractor, though. Have a gunsmith take a GOOD look at the rifle, incuding the chamber, locking lugs, etc; especially around the hole for the extractor pin in the bolt itself. Were you shooting handloaded or remanufactured ammo? A friend of mine blew up his rifle using handloads, so for me, that's a no-go. As I understand it, the difference between .223rem and 5.56 is in the CHAMBER dimensions, not the ammo itself, so to me, it doesn't sound like a problem that would be caused by using 556 in a 223 chamber.

I shot reloaded 223 ammo  In my ar, lapua brass, 22grains of vithavuory N120 and lapua 52 grs FMJ ammo. The case was blown at the base, but not separated, the extractor was bent, but not broken, the bolt carrier is ruptured at the base, while the bolt and the firing pin is really ok. The locking lugs are mostly ok, except of the one at 2'o clock, the one that intersect with the extractor, it's somewhat dinged from the impact the extractor did bending from hot gases.

I will soon post pictures.

I have had reloaded cases break all the way off about a 1/4" up from the bottom during extraction. I was lucky they did not blow out when fired. I went back through my reloads and found a visible ring you could see on some cases where the case was weakening. It was about their fourth loading.