I read everywhere high reps are needed for big traps, yet my mate who does no more than 6 reps on a huge ass weight, makes solid gains.
Let me know if you have tried both of these rep ranges. This is a real lagging body part for me.
Different rep ranges work for different people, this is because not everyone has the same ratio of white and red muscle fibers.
So rather than listen to what experts say or what has worked for someone else, you have to test what rep range works best for you.
One test is to first find out what you 1 rep max is and then after a rest take 80% of your 1RM and so as many reps as you can.
If you can only do low reps (4 to 6 for example) you would be better off doing low reps with a heavy weight for that body part.
If you can do medium reps (8 to 10 for example) you should do medium reps with a moderate weight for that body part.
If you can do high reps (12 to 15 for example) you should do high reps with a lighter weight for that body part.