I resurrected a thread from 2011 on this subject, and re-hosted all the broken photo links. That thread has photos of several different types of defective factory ammo, including a .45 ACP case with no rim. These photos are a real eye-opener for many folks, especially new shooters who haven't seen/fired very much ammo so far.
Thread can be found here:
Defective factory ammunition -- check your ammo, folks!
I'll repeat what Rex said, above, as it bears repeating: Inspect Your Ammo!
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)