Weathering Your Weapons
First you need some stuff: A 21st Century Toys 1/6th scale firearm, and a pencil.
Other tips like this, have you grind the pencil into powder, this is very messy, there is no way to avoid getting it on your hands.
I just rubbed the side of the pencil point onto the raised parts, on the AK I did this to the whole gun, making it look well used.
I raised the contrast on the pictures below to better see were the weathering was done.