Stop. Stop. Read this, or the “Guns” thread in the T-Cell.
Pull-ups and chin-ups are for lat width. They HAPPEN to offer bicep stimulation, but should never be used as a mainstay for a bicep exercise. Additionally, you need to make sure you’re hitting your arms from all angles. I’ll leave triceps out of it, but you should be doing a big, heavy bicep exercise for your bicep strength - such as a BB curl, and another slightly heavier one more focused towards isolation, like an EZ-bar preacher curl.
Additionally, doing things like hammer curls + k-pipe curls or variations of them with help work your brachi/brachioradialis and give the appearance of much bigger, fuller arms.
Stop. Doing. Chin-ups. For. Big. Arms.