Failure rates are basically a game of statistics...
And malfunctions are an inevitability, there is no such thing as a perfect functioning firearm, only one that hasn't malfunctioned yet.
This is where people get things wrong... one or two failures and the pistol is deemed not worthy? That's just statistical noise. It's predicted and expected. So long as any failures are very infrequent/rare and can't be shown to be caused by a mag or other problem. Basically, a problem that can't be directly attributed to some variable. That sort of random glitch happens... A well designed and put together gun minimizes the chances to as low a number as possible.
There is a reason the military has a "mean rounds between failure" spec. They know that a failre will eventually happen on occasion, so long as that they are rare and not persistent.
Most major issues show up quickly. Any that occurs after a longer period are probably caused by wear, though occasionally there are minor defects that take time to cause issues. But those are unpredictable... and no amount of function testing of the firearm will help, as the next round...
There are on occasion, infrequent random malfunctions, too close together to be truly random inevitable glitches, and too far apart to be easily explained or attributed to a cause... that can not be explained away... a malfunction every couple hundred rounds or so. Those are usually caused by things being just this side of wrong. Tolerance stacking, usually fixed by a different extractor. (As this is both an easy part to replace, and the most likely source of the problem)
For me...
After a few hundred trouble free rounds through the gun, spread around my carry mags... I call it good.
I put at least a box or two of my carry ammo though as well. And I only use factory ammo that I trust to be of good quality. Most stuff from the big names in ammo are fine.
I allow a couple malfunctions during the first box of rounds, but I will increase the amount of rounds I shoot another hundred during the evaluation phase, just to make sure.
I number my mags as well, so I can isolate bad ones.
