So what casings did Vance say were on the scene.
You aren’t suppose to use 556 in a 223 because of excessive pressure . Higher pressure than the chamber is designed for and can cause the primers to back out. Can cause the bullet to jam.
Don’t know if true or what this means . Just found it in the internet.
I wrote my previous before seeing your #120. Boy did I ever nail it.
Go read up on the differences. Brass is visually indistinguishable between the two unless you can read a head stamp.