Today, I went to my local academy looking for some random stuff (that I was unable to find...go figure!), but ended up snagging a pair of 8rd mags for my 1911.
Shortly after returning home, I did what needs to be done with each and every piece of new gear that gets acquired. TEST IT. When you buy a new mag (yes, even premium-quality gear like Magpul, Wilson Combat, HK, etc), they need to be tested. In addition to testing on the range during actual firing conditions, they need to be checked to ensure that the proper number of rounds will fit. They need to be function-checked to ensure that they feed properly.
Using proper safety precautions, load them up to capacity. Rack the slide. Does it feed? Does it feed smoothly and not hamper ejection, when you rack the slide again to feed another round? Does it feed every round in the mag? If the answer to each of these questions is "Yes", then your mag should function properly. All that's left is to take it to the range the next chance you get, and make sure it works under firing conditions.
The same holds true with all gear, of course. That holster you bought? How smoothly will it allow you to draw your weapon? When you are wearing your LBV and walking or running with it, does it reasonably stay in place? Are you comfortable in it? Is your gear set up where everything is easily-accessible? Is it making a lot of racket when you walk?
Just as important as function-checking your gear, you need to be function-checking your set-up. Just as important as function-checking your set-up, you need to be function-checking yourself.
There is an old adage that I've stolen from somewhere else on the interwebz, and I'm going to share it here once again...
"Amateurs train until they get it right, professionals train until they can't get it wrong."
Then again, we also have the saying used by Little League coaches every season throughout this nation...
"You're gonna play how you practice."
In other words, make sure your shit works.