The .308 and .243 are BOTH as close as I can measure 13mm deep, the .308 simply made a wider hole, interesting, as the metal is 12mm, so if you filed the bump flat on the back there would be 3 holes clean through the plate, due to the quality of the steel flexing I suspect.
The .223 is 6mm deep!
This could get deep and I don't know the answer, so how come the .243 with approx 50% more power than the .223 made a 13mm deep hole and wider as well?
And how come both the .308 made the same depth of hole as the .243 but wider still, when they were approx double the power of the .223??
O