After the high pressure round is fired, the bolt, barrel and/or chamber are checked for cracks and other damages. The round bolts from the 1960's that had the M marking were often advertised as Winchester (upsidedown M). The M meant the bolt was Magnetic Particle Tested or Magafluzed and no cracks were found. The punches and/or the P means the items were tested and passed.

I have the pressure of the different Test Rounds and the pressure is not the only difference. The types of powder change the pressure flow so the pressure is different from standard ammunition as the bullet travels though the rifling. I do not remember each one.

That high pressure test will show that normal ammunition will not hurt the tested item.

Hardness testing is usually part of production and will see that the item will not bent, break, or have other problems.