USGI mags get loaded 18 and 28, Pmags loaded full with covers on.
I have one particular 20 round USGI mag that lives in my truck. It’s been in 2 trucks now for almost 20 years. I’ve shot it, loaded it and stuck it right back in several times and never had a problem with it. That’s living in temps of over 100 degrees down to -0 a few times.
