Shelf life of some primer makes isn't very long. But you'll need a 1/4 MOA rifle and ammo plus a good shooter to see this happen. Wolf primers (from Russia) tend to have the longest life and are favored by many competitive shooters. The Russian factory, Murom Apparatus, that makes Wolf primers also has versions that are environmentally safe.
Powder degrades over time, but 20 years or so is typically a good estimate if stored in cool temperatures; heat's its worst enemy.
Biggest problem with stored reloads is the corrosion effect between the dissimilar metals of the case neck and bullet jacket. I've seen a couple of instances where very old reloads had such a bond between bullet and case mouth that the case mouth tore off the case shoulder and went out with the bullet when the round was fired. Rare, yes, but the fact that this situation could also change the bullet's release force needed to get it out of the case will effect peak pressure as well as accuracy and muzzle velocity. I've been told this is one reason why military arsenal ammo has an asphaltum sealant between case neck and bullet; prevents dissimilar metal corrosive bonding.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master