How much does a airsoft m16 mag hold?

It depends on if it is a mid or high cap magazine. Their are also low caps that are used for military purposes, they hold 30 rounds and are not meant for recreational or professional airsofters. Do not use them! Mid caps hold 120 rounds. High caps hold 350 rounds. Both of those numbers are specific to m16 btw. You can also get drum mags the can hold 2500 round and you can get them to be both manual wind and a battery powered wind.