I didn't know that EW didn't have many types of ammo !
The 2-3 EW rifles that you can snipe with only use microfusion cells . The fact that the ammo can be overcharged or max charged makes little difference against the target , overcharged cells will make the most damage against any target anyway
Whereas with gun ammos the differences between HP , AP and JHP are more marked , either of these can be more efficient against a specific type of target (unarmored , armoured , lightly armoured ) , so you'll choose the appropritae one to take out the target with just one shot .
With EW ammos , just always use overcharged microfusion cells and that's about it , if you use something else , then you'll make less damage . Besides , the Gauss is so overpowered when you character is skilled enough that there is no "real" need for using modified ammos to take down targets with just one shot , that's also why i rarely use the AMR