I haven't upgraded my gun either but most people go with:
- Longer Tightbore barrel (6.03 I believe hidden by a suppressor)
- Upgraded Springs
After those you're well on your way. There are other upgrades for AEG's but since you have a spring (or it appears to be a spring) then I'm not sure how to proceed after that.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE