You get the same amount of total ammo, just less in the mag, not a big deal really.
It's absolutely massive. CM from 100 to 50? My jolders went from 50 to 26? Vision?! It's a big deal mang
You obviously either didn't read the edits, or just don't play that much. It's a huge difference, plus your armor already maxed reserve ammo. The perk is absolutely useless.