Re: I have made a terrible mistake.
Here's a rule I follow for all my semi-auto magazine fed gun, pistols and rifles:
FACTORY MAGAZINES ONLY
Some times that is expensive but it completely eliminates the risk of getting crummy non-working magazines as I have gotten before this rule was in place, that got immediately got trashed.
For those who want a higher than 10 count magazine, that's tough here in California as none can be sold with more than a 10 round capacity. Some legal eagle here told some sellers at gun shows here in CA that they could sell magazine repair kits for older grandfathered larger capacity mags. So they disassemble a larger capacity magazine out of state and send it to CA as magazine parts which they sell in a package as a disassembled magazine. Works for me!