Quote Originally Posted by Soar View Post
The right being bigger makes sense, assuming you're right handed. Your arms will grow just don't over train.
Not necessarily. I am right handed and have a thicker and fuller looking left bicep, it also peaks more.

There are always genetic factors involved when it comes to symmetry.

OP: If you want your left bicep to catch up to your right bicep, here is a trick that most people aren't aware of and hence wouldn't be able to advice. When you do deadlifts, make sure your right hand is at the under-grip position in every set (especially heavy sets), this will allow the fascia to stretch more in that area, giving your right bicep more room to grow and peak eventually.