I'm not 100% sure on springs, but a lot of stress-cycle fatigue (S-N) graphs are logarithmic in nature, meaning a linear rate of increase in stress above the fatigue limit can shorten the life by consecutive orders of magnitude. In other words, if you stress it to level X, it may last 10,000 cycles; if you stress it to level X+1, it may last 1,000 cycles; if you stress it to level X+2, it may last 100 cycles, and so on. It could be that the 50rd Shockwave mags overstress the springs at 50rds, resulting in a short life. I believe OP mentioned he had around 2000rds on each magazine, which is only 40 loadings to full capacity. I'm using arbitrary numbers to demonstrate the point, but it could be that at maybe 45rds, they'll last 400 loadings. There are a lot of magazines out there that will hold more rounds than indicated, but that doesn't mean it is necessarily a good idea to cram those extra rounds in. Perhaps the Shockwave magazines would have been better off being labelled as 40rd or 45rd magazines to meet consumers' longevity expectations.