different round platforms. New (L) and old (R).
notice the curve of the magazines, the newer models curve more, see how the bottom of the older magazines straightens out?
there is no hole for the magazine catch in the newer model, from personal experience the catch would sometimes be too effective in keeping the magazine in the weapon, the newer mags were far easier to remove
different baseplates, the newer ones are slightly harder to remove which is good as the old ones could sometimes dislodge if you bash them about a bit
new spring and old, the newer one slightly longer, notice also how the round platform has longer 'legs' which means its easier to slide up and down inside the magazine, the old ones would get wedged and cause stoppages