100 shot of nitrous on 360 magnum engine

Most of your failure issues related to nitrous use are related to improper ring gap rather than just the piston material. Hyper slugs that came in stock magnums will handle the heat and pressure for what you're asking, but the rings being gapped too close will cause them to fail before the pistons metallurgically fail. This is of course assuming you take proper precautions regarding mixture, ignition timing, and activation conditions.

What is meant by activation conditions?