Is the shape of the muscle different? Have you injured one or the other? Did you ever play a one-side dominant sport (ie - baseball)?
May help answer the question. You could always do a couple of extra sets of DB curls with the smaller size.
My right shoulder is jacked - injured - and I played in high school, college, then semi-pro for a few years and my right biceps peak is not as good as my left (I through right handed) and I know it's from the injury, nerve damage, and also the constant elongation from throwing. Will probably never be completely symmetrical.
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Yup i have the same problem due to a shoulder injury. Like hossjob said throw in a couple more sets for the smaller arm or just add it in on another day until you feel you have balanced them out.
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Same here. Right handed and left bi is bigger. And I even had surgery to repair a completely torn biceps tendon and still it is bigger