Gun is original.
Reciever:
CAR-A3
HBAR Elite
Cal. 223
Ser. BK0
recommend that you feed it only .223 ammo, as marked on the barrel.
5.56 has similar exterior dimensions, but the brass itself is thicker, and works at higher pressures.
not that you couldn’t feed it 5.56 in a pinch.
my $.02 worth...
I like Federal in my match AR for just starting out.
I do reload for it with 69 Grain Sierra MatchKings, H335 powder and Winchester Primers.
Keep away from Wolf cartridges because of the heavy lacquer coating but any reputable cartridge will work fine.
Don’t be tempted to use the military cleaning rods. They will destroy that bore. Buy a good cleaning rod from a company called Dewey. You can order it from MidwayUSA.