Friend, blogger and photographer Oleg Volk (who also does the covers for my books) has put out a very valuable video warning of the dangers of bad ammunition. You'll find the details on his blog. I highly recommend clicking over there and watching the video. It's worth your time.
I second his warning enthusiastically. I've often been surprised by people who never test the ammunition they plan to rely on for their defense, if worse comes to worst. That can be as dangerous as having no ammunition at all. To illustrate, here are a few examples:
- Feeding problems have been reported with the US Army's new M855A1 service round. AR15.com has an informative thread about it, with pictures of how the round feeds through various magazines.
- Some guns run fine with ammunition from one manufacturer, but not with ammo from another. Here's just one example. Another, from my own experience: I have several boxes of Cor-Bon 9mm. 115gr. JHP +P ammunition (their original production rounds). It feeds and functions just fine through my Glock and Ruger pistols; but when a friend tried a box through a CZ pistol, he reported misfeed after misfeed.
- For legal liability reasons, I can't name it here: but I know of several law enforcement agencies that have stopped buying ammo from one major manufacturer because of what they describe as unacceptable variation in the velocity of its rounds. They've reported handgun rounds varying as much as 150 feet per second from each other, indicating inconsistent propellant loadings. This affects accuracy and terminal performance. They've decided (and I agree with them) that this is unacceptable in terms of officer safety, so they're now buying from other manufacturers. (I have older stocks of the ammunition they now distrust, bought some years ago, and they appear to perform as advertised; but I won't be buying any newer-production ammo from that company, either.) Interestingly, that same company's .22LR ammunition - previously well regarded - is now also gaining a reputation as a poor performer in terms of reliability. Perhaps they need to take a good, hard look at their production facilities and practices . . .
Massad Ayoob and others have long recommended a simple test: fire 200 rounds of your chosen defensive ammunition, through your chosen defensive handgun, using the magazines or reloading tools (e.g. speedloaders, etc.) that you're actually going to use to defend yourself, without a single malfunction, before you trust that combination with your life. I wholeheartedly endorse that test, and use it myself. (For guns that don't rely on semi-automatic function, such as revolvers or pump-action shotguns, I cut the round count down to 100.)
If you haven't performed that test with your defensive firearm(s) yet, I strongly recommend that you do so as quickly as possible. You might be surprised by the results . . . perhaps unpleasantly. If your gun can't do 200 trouble-free rounds with your chosen ammunition, try a different brand of ammunition. If it can't do 200 trouble-free rounds with two or more different brands of ammunition, get a better gun!