I recently went shooting with some friends and grabbed a Ruger Security 9 compact pro that I store in my car as a backup weapon. It was loaded with Critical Duty 9mm Ammo that was about 3 years old. The gun is stored pointed down in a holster and it had been a year since I cycled the Ammo. I was annoyed and later concerned to learn that every round resulted in a misfire. On further inspection, a light strike was present on each primer. I replaced the Ammo with junk I bought in bulk and experienced no problems the rest of the day.
I see four possible causes of the problem: temperature/ humidity, incompatible Ammo, vibration of the primer into the case, or problem with the firing pin. I tried the Ammo in two other identical pistols with one round firing. I shot identical ammo from the same lot that I store in a dark cool dry environment and had no problems. I would really like the problem to be vibration issues but welcome the opinions of others.
The problem remains: how do you stage or secure a pistol in your car and avoid causing problems with the Ammo?