Here's my old "swiss cheese" gong, it's 1/2" mild steel. Most of these complete pass throughs were with 7mm and bigger cartridges.
However, the vast majority of craters were made with little 24 or 25 calibers. Even at 400 and 500 yds, these little bullets put a pretty deep hole in the steel.
The 6" square plate on bottom is AR-500. The fresh shot is from 300 yds and shot with a 25-06.............WAY less damage
to the steel than before. Very glad I bought some.
Now I just need to find a 20-24 incher for my 1000 yd berm.