A Piezo pressure test is a modern method used to measure the internal pressure generated when a shotgun shell is fired. It employs a piezoelectric sensor, which contains a crystal that converts pressure changes into an electrical signal. This data helps manufacturers ensure the safety, reliability, and performance of their ammunition. 

The sensor is mounted in a test barrel, where it directly measures the pressure within the chamber during firing. Unlike older methods, such as the copper crusher system, the Piezo test provides highly accurate and immediate readings in units like pounds per square inch (psi) or megapascals (MPa). This allows for a precise pressure-versus-time profile of the ammunition’s performance, ensuring consistency and adherence to industry standards.

As for its effect on the shotgun shells, the test does not significantly alter or damage them. It may leave small marks or dimples on the hulls, but these do not compromise their structural integrity. The shells remain intact and usable after testing, making this method both effective and non-destructive.