I searched and couldn’t come up with anything solid for the life of me. I realize this topic is probably a dead horse on here so forgive me…
my armalite ar15 is marked 5.56 and is factory. can I shoot 5.56 ammo in it or will something unpleasant and painful happen?
You should be able to safely shoot anything marked 5.56 mm, 5.56 NATO, or .223 Remington.
Yes, this has been covered many times. Don’t worry, my search-fu if weak too.
thanks 
The important issue is whether or not you have a true 5.56 chamber as opposed to a .223 chamber. I would call Armalite and ask them directly. I am not sure what the current status is on their stuff.
Just because a barrel is marked 5.56 it does not mean that the chambers are the correct dimension. We have seen this alot with DPMS, Bushmaster, CMMG and others. Unsure whether or not they have fixed these issues.
just for general knowledge what would happen if it was a .223 chamber? would it jam or not feed at all?
The most common issue I’ve seen reported over the years is popped primers. You can fire a few rounds and inspect the primers for high pressure indicators… Excessive primer flattening, primer flow into the firing pin hole, etc.
ahh ok, My dad gifted me a bunch of xm193 so I wanted to check If I would explode if the gun wasn’t actually capable
Nah! If the round will chamber, you’re probably fine to fire some test rounds.
I’ve NEVER heard of a kabizzle from 5.56 in a .223 chamber. But you might get some complications.
shot about 350 rounds today of it with no problems. is it just me being crazy or does a 55g 5.56 kick a tad bit harder than a .223 55g bullet? I shot them back to back and it seemed the 5.56 had alittle more umph to it.
It’s loaded hotter, so yes you are right.