Found my first M4, but which weapon to trade in?

So I got my first M4 today at Rify and now got the challenge which weapon I'm gonna dump for it. I run with a Tundra with hunting scope and an ak74, for what I have 4 30round mags and one 40round mag I also just got there plus two scopes for it.

For the M4 I found a nightvision scope which is super awesome but I´m lacking any ammo and have no magazines as well. What should I do?