This is my experience, I have a mini 14 owned for 20yr. I have 5 20(factory) 30 rd mags. I have shot them all, have had a couple of FTF episodes, out of 1000+ rds., but that could be from the crap ammo I have used also.
My 30 rd mags were the cheapest I could get, and when I lived in Louisiana they got all rusty. I cleaned them up and use them and they work fine.
If I was going to take on the local drug cartel I would of course get the most reliable, expense no object, but I have not had much trouble.