556 is not the same as 223
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.
Do you understand the technical differences in the least? I can assure you I do, and as a practical matter for purposes of the discussion regarding Sandy Hook, 5.56 and .223 are interchangeable.
Minutia regarding chamber dimensions, brass thickness, and chamber pressures are not relevant issues here.