I think it's common. Last time I was measured for a custom shirt, my right bi was 19 7/8" and my left was 20 1/8". And I'm right handed. At times during pistol range training the rangemaster would say we were going to do a coarse of fire with our "weak hand". I told him I didn't have one. LOL
"I can't wait 'til tomorrow, 'cause I get stronger every day!"