TexasCHLforum.com

The good news is that, with modern ammunition the rounds in your gun aren't nearly as susceptible to environmental degradation as was WWII ammo. Alas, much of current "modern knowledge" (read, "myth") about ammo longevity comes from 60 years ago.

The two biggest enemies of ammunition are moisture and heat, in that order. It takes extended conditions over 140 degrees to do it, but constant exposure to that level of heat will start a slow degradation of the priming compound.

After a few years of storage in that kind of heat the primers--even with high quality, modern ammunition--could start to go bad. I recommend not waiting a few years to cycle through the ammo.