Hello, my name is Jim, 52 yrs old. I am new to the AR-15 world. (30 years ago, I use to eat, sleep and $%IT... with an M16A2) I just bought this AR-15 from an estate sale. Could someone help me figure out if it is 223 or 5.56. (I don't want to Load 5.56 if it's a 223 upper) It is a Bushmaster...