It's actually not just get all guns in a weapon class gold. you have to get every challenge done for every weapon in the class you want diamond for. So you'd have to get the guns gold and Maxed out after prestiging the gun twice.
https://www.youtube.com/user/gamelerp85?feature=mhee My youtube. I just started it, but am making gameplay vids. Nothing special. Check it out.
So if I wanted a diamond camo for assault rifle, I would have to get every assault riffle to gold status? That will take a while! SMH
It takes about two weeksish. For semi/busts use select fire because recoil = headshots. Gametypes don't matter so much just aim for the head. If you're really good to choas moshpit and backout until HQ/Hatdpoint/Demo matches, but only if you can get 30 kills rather than be the feeder.
The best part about video games is the youtube videos ~Everyone, 2012, the year of Our Lord.