I had a guy sell me a big box of NIW mags.  All but three were Center Ind. mags.  The other three were Coopers.  To get the big box, I had to take the entire lot to include the three Coopers.

My favorite range mag is an old Center 30.  It has been refinished three times and has a new GF and spring.  That old Center works 100% of the time.  It NEVER EVER fails.  It must have had 2000 rounds through it over the years and never a problem.  

Back to the Cooper....
So, I have these three Cooper mags.  What on earth do I do with them.  I don't even know if they will fit in the mag well.  Hence, I opened the bag on one, put in a new GF, loaded it, and off to the range.  The plan is to perhaps retire the trusty old Center mag that served me so well with this brand new perfect looking Cooper.  

The Coopers look perfect.  They have the correct number of welds, the construction looks just like all the others in my stash, no defects you can see.  For all the bad stuff I heard, I thought they looked great.   I put it in the mag. well at the range and it seemed a little tight, but nothing major.  I hit the bolt release....failure to feed.   Well that's just great.  After trying every trick in the book to make the damn thing work, I gave up.

I pulled out that old refinished Center and shot 120 rounds without a single problem.  

Perhaps all that stuff in the FAQs is true.