Ok. Ever wondered how to get flying xp without too much trouble? Well this is it.

Take desired weapon.
Go and start the heavy metal challenge.
At the beginning of final wave...jump in lava.
Now, instead of scrolling all the way down to find the challenge again...It's already on it!

I'm doing this and i only got 3 weapons left to get!!

That seems like a good way but endzone is better and here is how u do it

1. go to endzone
2. use your weapon a bit
3. get some turrets out and sit back
4. repeat

If you are leveling holoshield, then go to the tutorial level, get to the thing where you emp, but dont use it, get a holoshield out and stand behind it. use xp mods and the game wont keep up