Fully loaded mags dont wear springs, nuf said, thats been hit a few times here, as for only loading 28, I have always loaded full 30 and no problems. I own about 50 30 rnd mags and none of them give me problems with full loads, plus none of the many that I have used in the military either, having said that, some people do have this problem. I did have this happen once or twice but it was not the magazines, it turned out to be some dirt (very little) in the buffer tube, I cleaned it out, kept it dry, and voala, no problems. I think go with the most simple thing to fix first, try that.