How to make my biceps more solid?

Okay so i weight lift about 5 days a week. I do 3 sets of bicep curls except i do this thing where you start as if your going to do a hammer curl and then rotate your arm so it turns into a normal curl halfway through (apparently it makes your bicep wider). Anyway i do about 16 reps in each set. I also use the lat pull down (which i ume must be working them to some extent as well) and i also do 3 sets of 16 reps on my triceps. I take whey protein shakes after workout as well. Now my biceps are getting bigger but they dont feel very solid. My friend who started working out at the same time as me, has really solid feeling biceps even though he though he lifts 5 days a week as well. Any reason for this? Thanks